diff --git a/config/dbscheme-fragments.json b/config/dbscheme-fragments.json
new file mode 100644
index 000000000000..d3fae0127fa2
--- /dev/null
+++ b/config/dbscheme-fragments.json
@@ -0,0 +1,43 @@
+{
+  "files": [
+    "java/ql/lib/config/semmlecode.dbscheme",
+    "javascript/ql/lib/semmlecode.javascript.dbscheme",
+    "cpp/ql/lib/semmlecode.cpp.dbscheme",
+    "python/ql/lib/semmlecode.python.dbscheme",
+    "ruby/ql/lib/ruby.dbscheme",
+    "go/ql/lib/go.dbscheme",
+    "swift/prefix.dbscheme",
+    "swift/ql/lib/swift.dbscheme",
+    "csharp/ql/lib/semmlecode.csharp.dbscheme",
+    "ql/ql/src/ql.dbscheme"
+  ],
+  "fragments": [
+    "/*- Files and folders -*/",
+    "/*- Compilations -*/",
+    "/*- Compilations (Java) -*/",
+    "/*- Diagnostic messages -*/",
+    "/*- Duplicate code -*/",
+    "/*- External data -*/",
+    "/*- External packages -*/",
+    "/*- External defects and metrics -*/",
+    "/*- Source location prefix -*/",
+    "/*- Lines of code -*/",
+    "/*- Snapshot date -*/",
+    "/*- Version control data -*/",
+    "/*- YAML -*/",
+    "/*- XML Files -*/",
+    "/*- SMAP -*/",
+    "/*- Java -*/",
+    "/*- configuration files with key value pairs -*/",
+    "/*- Kotlin -*/",
+    "/*- JavaScript-specific part -*/",
+    "/*- Ruby-specific part -*/",
+    "/*- ERB-specific part -*/",
+    "/*- GO-specific part -*/",
+    "/*- QL-specific part -*/",
+    "/*- Swift-specific part -*/",
+    "/*- C# dbscheme -*/",
+    "/*- C++ dbscheme -*/",
+    "/*- Python dbscheme -*/"
+  ]
+}
\ No newline at end of file
diff --git a/config/sync-dbscheme-fragments.py b/config/sync-dbscheme-fragments.py
new file mode 100755
index 000000000000..b6019544be81
--- /dev/null
+++ b/config/sync-dbscheme-fragments.py
@@ -0,0 +1,59 @@
+#!/usr/bin/env python3
+
+import json
+import os
+import re
+import itertools
+
+def make_groups(blocks):
+    groups = {}
+    for block in blocks:
+        groups.setdefault("".join(block["lines"]), []).append(block)
+    return list(groups.values())
+
+def validate_fragments(fragments):
+    for header, blocks in fragments.items():
+        groups = make_groups(blocks)
+        if len(groups) > 1:
+            print("Warning: '{}' fragments are different for {}".format(header, ["{}:{}:{}".format(group[0]["file"], group[0]["start"], group[0]["end"]) for group in groups]))
+
+def main():
+    script_dir = os.path.dirname(os.path.realpath(__file__))
+
+    with open(os.path.join(script_dir, "dbscheme-fragments.json"), "r") as f:
+        config = json.load(f)
+
+    fragment_headers = set(config["fragments"])
+    fragments = {}
+    for file in config["files"]:
+        with open(os.path.join(os.path.dirname(script_dir), file), "r") as dbscheme:
+            header = None
+            line_number = 1
+            block = { "file": file, "start": line_number, "end": None, "lines": [] }
+            def end_block():
+                nonlocal header, block, line_number, fragments
+                block["end"] = line_number - 1
+                if len(block["lines"]) > 0:
+                    if header is None:
+                        if re.match(r'(?m)^//.*$|/\*(\**[^\*])*\*+/', "".join(block["lines"])):
+                            # Ignore comments at the beginning of the file
+                            pass
+                        else:                            
+                            print("Warning: fragment without header: {}:{}:{}".format(block["file"], block["start"], block["end"]))
+                    else:
+                        fragments.setdefault(header, []).append(block)
+            for line in dbscheme:
+                m = re.match(r"^\/\*-.*-\*\/$", line)
+                if m:
+                    end_block()
+                    header = line.strip()
+                    if header not in fragment_headers:
+                        print("Warning: unknown fragment header: {}: {}:{}".format(header, file, line_number))
+                    block = { "file": file, "start": line_number, "end": None, "lines": [] }
+                block["lines"].append(line)
+                line_number += 1
+            end_block()
+    validate_fragments(fragments)
+
+if __name__ == "__main__":
+    main()
diff --git a/cpp/ql/lib/semmlecode.cpp.dbscheme b/cpp/ql/lib/semmlecode.cpp.dbscheme
index 19887dbd3332..9a8aa05ae606 100644
--- a/cpp/ql/lib/semmlecode.cpp.dbscheme
+++ b/cpp/ql/lib/semmlecode.cpp.dbscheme
@@ -1,3 +1,4 @@
+/*- Compilations -*/
 
 /**
  * An invocation of the compiler. Note that more than one file may be
@@ -10,118 +11,119 @@
  * directory from which the compiler was invoked.
  */
 compilations(
-    /**
-     * An invocation of the compiler. Note that more than one file may
-     * be compiled per invocation. For example, this command compiles
-     * three source files:
-     *
-     *   gcc -c f1.c f2.c f3.c
-     */
-    unique int id : @compilation,
-    string cwd : string ref
+  /**
+   * An invocation of the compiler. Note that more than one file may
+   * be compiled per invocation. For example, this command compiles
+   * three source files:
+   *
+   *   gcc -c f1.c f2.c f3.c
+   */
+  unique int id : @compilation,
+  string cwd : string ref
 );
 
 /**
- * The arguments that were passed to the extractor for a compiler
- * invocation. If `id` is for the compiler invocation
- *
- *   gcc -c f1.c f2.c f3.c
- *
- * then typically there will be rows for
- *
- * num | arg
- * --- | ---
- * 0   | *path to extractor*
- * 1   | `--mimic`
- * 2   | `/usr/bin/gcc`
- * 3   | `-c`
- * 4   | f1.c
- * 5   | f2.c
- * 6   | f3.c
- */
+* The arguments that were passed to the extractor for a compiler
+* invocation. If `id` is for the compiler invocation
+*
+*   gcc -c f1.c f2.c f3.c
+*
+* then typically there will be rows for
+*
+* num | arg
+* --- | ---
+* 0   | *path to extractor*
+* 1   | `--mimic`
+* 2   | `/usr/bin/gcc`
+* 3   | `-c`
+* 4   | f1.c
+* 5   | f2.c
+* 6   | f3.c
+*/
 #keyset[id, num]
 compilation_args(
-    int id : @compilation ref,
-    int num : int ref,
-    string arg : string ref
+  int id : @compilation ref,
+  int num : int ref,
+  string arg : string ref
 );
 
 /**
- * The source files that are compiled by a compiler invocation.
- * If `id` is for the compiler invocation
- *
- *   gcc -c f1.c f2.c f3.c
- *
- * then there will be rows for
- *
- * num | arg
- * --- | ---
- * 0   | f1.c
- * 1   | f2.c
- * 2   | f3.c
- *
- * Note that even if those files `#include` headers, those headers
- * do not appear as rows.
- */
+* The source files that are compiled by a compiler invocation.
+* If `id` is for the compiler invocation
+*
+*   gcc -c f1.c f2.c f3.c
+*
+* then there will be rows for
+*
+* num | arg
+* --- | ---
+* 0   | f1.c
+* 1   | f2.c
+* 2   | f3.c
+*
+* Note that even if those files `#include` headers, those headers
+* do not appear as rows.
+*/
 #keyset[id, num]
 compilation_compiling_files(
-    int id : @compilation ref,
-    int num : int ref,
-    int file : @file ref
+  int id : @compilation ref,
+  int num : int ref,
+  int file : @file ref
 );
 
 /**
- * The time taken by the extractor for a compiler invocation.
- *
- * For each file `num`, there will be rows for
- *
- * kind | seconds
- * ---- | ---
- * 1    | CPU seconds used by the extractor frontend
- * 2    | Elapsed seconds during the extractor frontend
- * 3    | CPU seconds used by the extractor backend
- * 4    | Elapsed seconds during the extractor backend
- */
+* The time taken by the extractor for a compiler invocation.
+*
+* For each file `num`, there will be rows for
+*
+* kind | seconds
+* ---- | ---
+* 1    | CPU seconds used by the extractor frontend
+* 2    | Elapsed seconds during the extractor frontend
+* 3    | CPU seconds used by the extractor backend
+* 4    | Elapsed seconds during the extractor backend
+*/
 #keyset[id, num, kind]
 compilation_time(
-    int id : @compilation ref,
-    int num : int ref,
-    /* kind:
-       1 = frontend_cpu_seconds
-       2 = frontend_elapsed_seconds
-       3 = extractor_cpu_seconds
-       4 = extractor_elapsed_seconds
-    */
-    int kind : int ref,
-    float seconds : float ref
+  int id : @compilation ref,
+  int num : int ref,
+  /* kind:
+     1 = frontend_cpu_seconds
+     2 = frontend_elapsed_seconds
+     3 = extractor_cpu_seconds
+     4 = extractor_elapsed_seconds
+  */
+  int kind : int ref,
+  float seconds : float ref
 );
 
 /**
- * An error or warning generated by the extractor.
- * The diagnostic message `diagnostic` was generated during compiler
- * invocation `compilation`, and is the `file_number_diagnostic_number`th
- * message generated while extracting the `file_number`th file of that
- * invocation.
- */
+* An error or warning generated by the extractor.
+* The diagnostic message `diagnostic` was generated during compiler
+* invocation `compilation`, and is the `file_number_diagnostic_number`th
+* message generated while extracting the `file_number`th file of that
+* invocation.
+*/
 #keyset[compilation, file_number, file_number_diagnostic_number]
 diagnostic_for(
-    int diagnostic : @diagnostic ref,
-    int compilation : @compilation ref,
-    int file_number : int ref,
-    int file_number_diagnostic_number : int ref
+  int diagnostic : @diagnostic ref,
+  int compilation : @compilation ref,
+  int file_number : int ref,
+  int file_number_diagnostic_number : int ref
 );
 
 /**
- * If extraction was successful, then `cpu_seconds` and
- * `elapsed_seconds` are the CPU time and elapsed time (respectively)
- * that extraction took for compiler invocation `id`.
- */
+* If extraction was successful, then `cpu_seconds` and
+* `elapsed_seconds` are the CPU time and elapsed time (respectively)
+* that extraction took for compiler invocation `id`.
+*/
 compilation_finished(
-    unique int id : @compilation ref,
-    float cpu_seconds : float ref,
-    float elapsed_seconds : float ref
+  unique int id : @compilation ref,
+  float cpu_seconds : float ref,
+  float elapsed_seconds : float ref
 );
 
+/*- External data -*/
 
 /**
  * External data, loaded from CSV files during snapshot creation. See
@@ -129,17 +131,21 @@ compilation_finished(
  * for more information.
  */
 externalData(
-    int id : @externalDataElement,
-    string path : string ref,
-    int column: int ref,
-    string value : string ref
+  int id : @externalDataElement,
+  string path : string ref,
+  int column: int ref,
+  string value : string ref
 );
 
+/*- Source location prefix -*/
+
 /**
  * The source location of the snapshot.
  */
 sourceLocationPrefix(string prefix : string ref);
 
+/*- External packages -*/
+
 /**
  * Information about packages that provide code used during compilation.
  * The `id` is just a unique identifier.
@@ -163,41 +169,35 @@ header_to_external_package(
     int package : @external_package ref
 );
 
-/*
- * Version history
- */
+/*- Version control data -*/
 
 svnentries(
-    unique int id : @svnentry,
-    string revision : string ref,
-    string author : string ref,
-    date revisionDate : date ref,
-    int changeSize : int ref
+  unique int id : @svnentry,
+  string revision : string ref,
+  string author : string ref,
+  date revisionDate : date ref,
+  int changeSize : int ref
 )
 
 svnaffectedfiles(
-    int id : @svnentry ref,
-    int file : @file ref,
-    string action : string ref
+  int id : @svnentry ref,
+  int file : @file ref,
+  string action : string ref
 )
 
 svnentrymsg(
-    unique int id : @svnentry ref,
-    string message : string ref
+  unique int id : @svnentry ref,
+  string message : string ref
 )
 
 svnchurn(
-    int commit : @svnentry ref,
-    int file : @file ref,
-    int addedLines : int ref,
-    int deletedLines : int ref
+  int commit : @svnentry ref,
+  int file : @file ref,
+  int addedLines : int ref,
+  int deletedLines : int ref
 )
 
-/*
- * C++ dbscheme
- */
-
-@location = @location_stmt | @location_expr | @location_default ;
+/*- Files and folders -*/
 
 /**
  * The location of an element that is not an expression or a statement.
@@ -207,15 +207,62 @@ svnchurn(
  * [Locations](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
  */
 locations_default(
-    /** The location of an element that is not an expression or a statement. */
-    unique int id: @location_default,
-    int container: @container ref,
-    int startLine: int ref,
-    int startColumn: int ref,
-    int endLine: int ref,
-    int endColumn: int ref
+  /** The location of an element that is not an expression or a statement. */
+  unique int id: @location_default,
+  int container: @container ref,
+  int startLine: int ref,
+  int startColumn: int ref,
+  int endLine: int ref,
+  int endColumn: int ref
 );
 
+files(
+  unique int id: @file,
+  string name: string ref
+);
+
+folders(
+  unique int id: @folder,
+  string name: string ref
+);
+
+@container = @file | @folder
+
+containerparent(
+  int parent: @container ref,
+  unique int child: @container ref
+);
+
+/*- Lines of code -*/
+
+#keyset[element_id]
+numlines(
+  int element_id: @sourceline ref,
+  int num_lines: int ref,
+  int num_code: int ref,
+  int num_comment: int ref
+);
+
+/*- Diagnostic messages -*/
+
+diagnostics(
+  unique int id: @diagnostic,
+  int severity: int ref,
+  string error_tag: string ref,
+  string error_message: string ref,
+  string full_error_message: string ref,
+  int location: @location_default ref
+);
+
+case @diagnostic.severity of
+  10 = @diagnostic_debug
+| 20 = @diagnostic_info
+| 30 = @diagnostic_warning
+| 40 = @diagnostic_error
+;
+
+/*- C++ dbscheme -*/
+
 /**
  * The location of a statement.
  * The location spans column `startcolumn` of line `startline` to
@@ -253,38 +300,7 @@ locations_expr(
 /** An element for which line-count information is available. */
 @sourceline = @file | @function | @variable | @enumconstant | @xmllocatable;
 
-numlines(
-    int element_id: @sourceline ref,
-    int num_lines: int ref,
-    int num_code: int ref,
-    int num_comment: int ref
-);
-
-diagnostics(
-    unique int id: @diagnostic,
-    int severity: int ref,
-    string error_tag: string ref,
-    string error_message: string ref,
-    string full_error_message: string ref,
-    int location: @location_default ref
-);
-
-files(
-    unique int id: @file,
-    string name: string ref
-);
-
-folders(
-    unique int id: @folder,
-    string name: string ref
-);
-
-@container = @folder | @file
-
-containerparent(
-    int parent: @container ref,
-    unique int child: @container ref
-);
+@location = @location_stmt | @location_expr | @location_default ;
 
 fileannotations(
     int id: @file ref,
@@ -2137,76 +2153,74 @@ link_parent(
     int link_target : @link_target ref
 );
 
-/* XML Files */
+/*- XML Files -*/
 
-xmlEncoding(unique int id: @file ref, string encoding: string ref);
+xmlEncoding(
+  unique int id: @file ref,
+  string encoding: string ref
+);
 
 xmlDTDs(
-    unique int id: @xmldtd,
-    string root: string ref,
-    string publicId: string ref,
-    string systemId: string ref,
-    int fileid: @file ref
+  unique int id: @xmldtd,
+  string root: string ref,
+  string publicId: string ref,
+  string systemId: string ref,
+  int fileid: @file ref
 );
 
 xmlElements(
-    unique int id: @xmlelement,
-    string name: string ref,
-    int parentid: @xmlparent ref,
-    int idx: int ref,
-    int fileid: @file ref
+  unique int id: @xmlelement,
+  string name: string ref,
+  int parentid: @xmlparent ref,
+  int idx: int ref,
+  int fileid: @file ref
 );
 
 xmlAttrs(
-    unique int id: @xmlattribute,
-    int elementid: @xmlelement ref,
-    string name: string ref,
-    string value: string ref,
-    int idx: int ref,
-    int fileid: @file ref
+  unique int id: @xmlattribute,
+  int elementid: @xmlelement ref,
+  string name: string ref,
+  string value: string ref,
+  int idx: int ref,
+  int fileid: @file ref
 );
 
 xmlNs(
-    int id: @xmlnamespace,
-    string prefixName: string ref,
-    string URI: string ref,
-    int fileid: @file ref
+  int id: @xmlnamespace,
+  string prefixName: string ref,
+  string URI: string ref,
+  int fileid: @file ref
 );
 
 xmlHasNs(
-    int elementId: @xmlnamespaceable ref,
-    int nsId: @xmlnamespace ref,
-    int fileid: @file ref
+  int elementId: @xmlnamespaceable ref,
+  int nsId: @xmlnamespace ref,
+  int fileid: @file ref
 );
 
 xmlComments(
-    unique int id: @xmlcomment,
-    string text: string ref,
-    int parentid: @xmlparent ref,
-    int fileid: @file ref
+  unique int id: @xmlcomment,
+  string text: string ref,
+  int parentid: @xmlparent ref,
+  int fileid: @file ref
 );
 
 xmlChars(
-    unique int id: @xmlcharacters,
-    string text: string ref,
-    int parentid: @xmlparent ref,
-    int idx: int ref,
-    int isCDATA: int ref,
-    int fileid: @file ref
+  unique int id: @xmlcharacters,
+  string text: string ref,
+  int parentid: @xmlparent ref,
+  int idx: int ref,
+  int isCDATA: int ref,
+  int fileid: @file ref
 );
 
 @xmlparent = @file | @xmlelement;
 @xmlnamespaceable = @xmlelement | @xmlattribute;
 
 xmllocations(
-    int xmlElement: @xmllocatable ref,
-    int location: @location_default ref
+  int xmlElement: @xmllocatable ref,
+  int location: @location_default ref
 );
 
-@xmllocatable = @xmlcharacters
-              | @xmlelement
-              | @xmlcomment
-              | @xmlattribute
-              | @xmldtd
-              | @file
-              | @xmlnamespace;
+@xmllocatable = @xmlcharacters | @xmlelement | @xmlcomment | @xmlattribute | @xmldtd | @file | @xmlnamespace;
+
diff --git a/csharp/ql/lib/semmlecode.csharp.dbscheme b/csharp/ql/lib/semmlecode.csharp.dbscheme
index cd877b8cc2fb..5981e383e872 100644
--- a/csharp/ql/lib/semmlecode.csharp.dbscheme
+++ b/csharp/ql/lib/semmlecode.csharp.dbscheme
@@ -9,65 +9,289 @@
  * mechanism not work properly.
  */
 
+/*- Compilations -*/
+
 /**
  * An invocation of the compiler. Note that more than one file may be
  * compiled per invocation. For example, this command compiles three
  * source files:
  *
- *   csc f1.cs f2.cs f3.cs
+ *   gcc -c f1.c f2.c f3.c
  *
  * The `id` simply identifies the invocation, while `cwd` is the working
  * directory from which the compiler was invoked.
  */
 compilations(
-    unique int id : @compilation,
-    string cwd : string ref
+  /**
+   * An invocation of the compiler. Note that more than one file may
+   * be compiled per invocation. For example, this command compiles
+   * three source files:
+   *
+   *   gcc -c f1.c f2.c f3.c
+   */
+  unique int id : @compilation,
+  string cwd : string ref
 );
 
 /**
- * The arguments that were passed to the extractor for a compiler
- * invocation. If `id` is for the compiler invocation
- *
- *   csc f1.cs f2.cs f3.cs
- *
- * then typically there will be rows for
- *
- * num | arg
- * --- | ---
- * 0   | --compiler
- * 1   | *path to compiler*
- * 2   | f1.cs
- * 3   | f2.cs
- * 4   | f3.cs
- */
+* The arguments that were passed to the extractor for a compiler
+* invocation. If `id` is for the compiler invocation
+*
+*   gcc -c f1.c f2.c f3.c
+*
+* then typically there will be rows for
+*
+* num | arg
+* --- | ---
+* 0   | *path to extractor*
+* 1   | `--mimic`
+* 2   | `/usr/bin/gcc`
+* 3   | `-c`
+* 4   | f1.c
+* 5   | f2.c
+* 6   | f3.c
+*/
 #keyset[id, num]
 compilation_args(
-    int id : @compilation ref,
-    int num : int ref,
-    string arg : string ref
+  int id : @compilation ref,
+  int num : int ref,
+  string arg : string ref
 );
 
 /**
- * The source files that are compiled by a compiler invocation.
- * If `id` is for the compiler invocation
- *
- *   csc f1.cs f2.cs f3.cs
- *
- * then there will be rows for
- *
- * num | arg
- * --- | ---
- * 0   | f1.cs
- * 1   | f2.cs
- * 2   | f3.cs
- */
+* The source files that are compiled by a compiler invocation.
+* If `id` is for the compiler invocation
+*
+*   gcc -c f1.c f2.c f3.c
+*
+* then there will be rows for
+*
+* num | arg
+* --- | ---
+* 0   | f1.c
+* 1   | f2.c
+* 2   | f3.c
+*
+* Note that even if those files `#include` headers, those headers
+* do not appear as rows.
+*/
 #keyset[id, num]
 compilation_compiling_files(
-    int id : @compilation ref,
-    int num : int ref,
-    int file : @file ref
+  int id : @compilation ref,
+  int num : int ref,
+  int file : @file ref
+);
+
+/**
+* The time taken by the extractor for a compiler invocation.
+*
+* For each file `num`, there will be rows for
+*
+* kind | seconds
+* ---- | ---
+* 1    | CPU seconds used by the extractor frontend
+* 2    | Elapsed seconds during the extractor frontend
+* 3    | CPU seconds used by the extractor backend
+* 4    | Elapsed seconds during the extractor backend
+*/
+#keyset[id, num, kind]
+compilation_time(
+  int id : @compilation ref,
+  int num : int ref,
+  /* kind:
+     1 = frontend_cpu_seconds
+     2 = frontend_elapsed_seconds
+     3 = extractor_cpu_seconds
+     4 = extractor_elapsed_seconds
+  */
+  int kind : int ref,
+  float seconds : float ref
+);
+
+/**
+* An error or warning generated by the extractor.
+* The diagnostic message `diagnostic` was generated during compiler
+* invocation `compilation`, and is the `file_number_diagnostic_number`th
+* message generated while extracting the `file_number`th file of that
+* invocation.
+*/
+#keyset[compilation, file_number, file_number_diagnostic_number]
+diagnostic_for(
+  int diagnostic : @diagnostic ref,
+  int compilation : @compilation ref,
+  int file_number : int ref,
+  int file_number_diagnostic_number : int ref
+);
+
+/**
+* If extraction was successful, then `cpu_seconds` and
+* `elapsed_seconds` are the CPU time and elapsed time (respectively)
+* that extraction took for compiler invocation `id`.
+*/
+compilation_finished(
+  unique int id : @compilation ref,
+  float cpu_seconds : float ref,
+  float elapsed_seconds : float ref
+);
+
+/*- Diagnostic messages -*/
+
+diagnostics(
+  unique int id: @diagnostic,
+  int severity: int ref,
+  string error_tag: string ref,
+  string error_message: string ref,
+  string full_error_message: string ref,
+  int location: @location_default ref
 );
 
+case @diagnostic.severity of
+  10 = @diagnostic_debug
+| 20 = @diagnostic_info
+| 30 = @diagnostic_warning
+| 40 = @diagnostic_error
+;
+
+/*- External data -*/
+
+/**
+ * External data, loaded from CSV files during snapshot creation. See
+ * [Tutorial: Incorporating external data](https://help.semmle.com/wiki/display/SD/Tutorial%3A+Incorporating+external+data)
+ * for more information.
+ */
+externalData(
+  int id : @externalDataElement,
+  string path : string ref,
+  int column: int ref,
+  string value : string ref
+);
+
+/*- Source location prefix -*/
+
+/**
+ * The source location of the snapshot.
+ */
+sourceLocationPrefix(string prefix : string ref);
+
+/*- Files and folders -*/
+
+/**
+ * The location of an element that is not an expression or a statement.
+ * The location spans column `startcolumn` of line `startline` to
+ * column `endcolumn` of line `endline` in file `file`.
+ * For more information, see
+ * [Locations](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
+ */
+locations_default(
+  /** The location of an element that is not an expression or a statement. */
+  unique int id: @location_default,
+  int container: @container ref,
+  int startLine: int ref,
+  int startColumn: int ref,
+  int endLine: int ref,
+  int endColumn: int ref
+);
+
+files(
+  unique int id: @file,
+  string name: string ref
+);
+
+folders(
+  unique int id: @folder,
+  string name: string ref
+);
+
+@container = @file | @folder
+
+containerparent(
+  int parent: @container ref,
+  unique int child: @container ref
+);
+
+/*- Lines of code -*/
+
+#keyset[element_id]
+numlines(
+  int element_id: @sourceline ref,
+  int num_lines: int ref,
+  int num_code: int ref,
+  int num_comment: int ref
+);
+
+/*- XML Files -*/
+
+xmlEncoding(
+  unique int id: @file ref,
+  string encoding: string ref
+);
+
+xmlDTDs(
+  unique int id: @xmldtd,
+  string root: string ref,
+  string publicId: string ref,
+  string systemId: string ref,
+  int fileid: @file ref
+);
+
+xmlElements(
+  unique int id: @xmlelement,
+  string name: string ref,
+  int parentid: @xmlparent ref,
+  int idx: int ref,
+  int fileid: @file ref
+);
+
+xmlAttrs(
+  unique int id: @xmlattribute,
+  int elementid: @xmlelement ref,
+  string name: string ref,
+  string value: string ref,
+  int idx: int ref,
+  int fileid: @file ref
+);
+
+xmlNs(
+  int id: @xmlnamespace,
+  string prefixName: string ref,
+  string URI: string ref,
+  int fileid: @file ref
+);
+
+xmlHasNs(
+  int elementId: @xmlnamespaceable ref,
+  int nsId: @xmlnamespace ref,
+  int fileid: @file ref
+);
+
+xmlComments(
+  unique int id: @xmlcomment,
+  string text: string ref,
+  int parentid: @xmlparent ref,
+  int fileid: @file ref
+);
+
+xmlChars(
+  unique int id: @xmlcharacters,
+  string text: string ref,
+  int parentid: @xmlparent ref,
+  int idx: int ref,
+  int isCDATA: int ref,
+  int fileid: @file ref
+);
+
+@xmlparent = @file | @xmlelement;
+@xmlnamespaceable = @xmlelement | @xmlattribute;
+
+xmllocations(
+  int xmlElement: @xmllocatable ref,
+  int location: @location_default ref
+);
+
+@xmllocatable = @xmlcharacters | @xmlelement | @xmlcomment | @xmlattribute | @xmldtd | @file | @xmlnamespace;
+
+/*- C# dbscheme -*/
+
 /**
  * The references used by a compiler invocation.
  * If `id` is for the compiler invocation
@@ -89,96 +313,22 @@ compilation_referencing_files(
     int file : @file ref
 );
 
-/**
- * The time taken by the extractor for a compiler invocation.
- *
- * For each file `num`, there will be rows for
- *
- * kind | seconds
- * ---- | ---
- * 1    | CPU seconds used by the extractor frontend
- * 2    | Elapsed seconds during the extractor frontend
- * 3    | CPU seconds used by the extractor backend
- * 4    | Elapsed seconds during the extractor backend
- */
-#keyset[id, num, kind]
-compilation_time(
-    int id : @compilation ref,
-    int num : int ref,
-    /* kind:
-       1 = frontend_cpu_seconds
-       2 = frontend_elapsed_seconds
-       3 = extractor_cpu_seconds
-       4 = extractor_elapsed_seconds
-    */
-    int kind : int ref,
-    float seconds : float ref
-);
-
-/**
- * An error or warning generated by the extractor.
- * The diagnostic message `diagnostic` was generated during compiler
- * invocation `compilation`, and is the `file_number_diagnostic_number`th
- * message generated while extracting the `file_number`th file of that
- * invocation.
- */
-#keyset[compilation, file_number, file_number_diagnostic_number]
-diagnostic_for(
-    unique int diagnostic : @diagnostic ref,
-    int compilation : @compilation ref,
-    int file_number : int ref,
-    int file_number_diagnostic_number : int ref
-);
-
-diagnostics(
-    unique int id: @diagnostic,
-    int severity: int ref,
-    string error_tag: string ref,
-    string error_message: string ref,
-    string full_error_message: string ref,
-    int location: @location_default ref
-);
-
 extractor_messages(
-    unique int id: @extractor_message,
-    int severity: int ref,
-    string origin : string ref,
-    string text : string ref,
-    string entity : string ref,
-    int location: @location_default ref,
-    string stack_trace : string ref
+  unique int id: @extractor_message,
+  int severity: int ref,
+  string origin : string ref,
+  string text : string ref,
+  string entity : string ref,
+  int location: @location_default ref,
+  string stack_trace : string ref
 );
 
-/**
- * If extraction was successful, then `cpu_seconds` and
- * `elapsed_seconds` are the CPU time and elapsed time (respectively)
- * that extraction took for compiler invocation `id`.
- */
-compilation_finished(
-    unique int id : @compilation ref,
-    float cpu_seconds : float ref,
-    float elapsed_seconds : float ref
-);
 
 compilation_assembly(
-  unique int id : @compilation ref,
-  int assembly: @assembly ref
+unique int id : @compilation ref,
+int assembly: @assembly ref
 )
 
-// Populated by the CSV extractor
-externalData(
-   int id: @externalDataElement,
-   string path: string ref,
-   int column: int ref,
-   string value: string ref);
-
-sourceLocationPrefix(
-  string prefix: string ref);
-
-/*
- * C# dbscheme
- */
-
 /** ELEMENTS **/
 
 @element = @declaration | @stmt | @expr | @modifier | @attribute | @namespace_declaration
@@ -203,26 +353,12 @@ sourceLocationPrefix(
 
 @location = @location_default | @assembly;
 
-locations_default(
-  unique int id: @location_default,
-  int file: @file ref,
-  int beginLine: int ref,
-  int beginColumn: int ref,
-  int endLine: int ref,
-  int endColumn: int ref);
-
 locations_mapped(
   unique int id: @location_default ref,
   int mapped_to: @location_default ref);
 
 @sourceline = @file | @callable | @xmllocatable;
 
-numlines(
-  int element_id: @sourceline ref,
-  int num_lines: int ref,
-  int num_code: int ref,
-  int num_comment: int ref);
-
 assemblies(
   unique int id: @assembly,
   int file: @file ref,
@@ -230,20 +366,6 @@ assemblies(
   string name: string ref,
   string version: string ref);
 
-files(
-  unique int id: @file,
-  string name: string ref);
-
-folders(
-  unique int id: @folder,
-  string name: string ref);
-
-@container = @folder | @file ;
-
-containerparent(
-  int parent: @container ref,
-  unique int child: @container ref);
-
 file_extraction_mode(
   unique int file: @file ref,
   int mode: int ref
@@ -1297,68 +1419,6 @@ lambda_expr_return_type(
 
 @control_flow_element = @stmt | @expr;
 
-/* XML Files */
-
-xmlEncoding  (
-  unique int id: @file ref,
-  string encoding: string ref);
-
-xmlDTDs(
-  unique int id: @xmldtd,
-  string root: string ref,
-  string publicId: string ref,
-  string systemId: string ref,
-  int fileid: @file ref);
-
-xmlElements(
-  unique int id: @xmlelement,
-  string name: string ref,
-  int parentid: @xmlparent ref,
-  int idx: int ref,
-  int fileid: @file ref);
-
-xmlAttrs(
-  unique int id: @xmlattribute,
-  int elementid: @xmlelement ref,
-  string name: string ref,
-  string value: string ref,
-  int idx: int ref,
-  int fileid: @file ref);
-
-xmlNs(
-  int id: @xmlnamespace,
-  string prefixName: string ref,
-  string URI: string ref,
-  int fileid: @file ref);
-
-xmlHasNs(
-  int elementId: @xmlnamespaceable ref,
-  int nsId: @xmlnamespace ref,
-  int fileid: @file ref);
-
-xmlComments(
-  unique int id: @xmlcomment,
-  string text: string ref,
-  int parentid: @xmlparent ref,
-  int fileid: @file ref);
-
-xmlChars(
-  unique int id: @xmlcharacters,
-  string text: string ref,
-  int parentid: @xmlparent ref,
-  int idx: int ref,
-  int isCDATA: int ref,
-  int fileid: @file ref);
-
-@xmlparent = @file | @xmlelement;
-@xmlnamespaceable = @xmlelement | @xmlattribute;
-
-xmllocations(
-  int xmlElement: @xmllocatable ref,
-  int location: @location_default ref);
-
-@xmllocatable = @xmlcharacters | @xmlelement | @xmlcomment | @xmlattribute | @xmldtd | @file | @xmlnamespace;
-
 /* Comments */
 
 commentline(
diff --git a/go/ql/lib/go.dbscheme b/go/ql/lib/go.dbscheme
index a58b81b1b4c4..b299d649c0c3 100644
--- a/go/ql/lib/go.dbscheme
+++ b/go/ql/lib/go.dbscheme
@@ -1,19 +1,20 @@
 /** Auto-generated dbscheme; do not edit. */
 
-
-/** Duplicate code **/
+/*- Duplicate code -*/
 
 duplicateCode(
   unique int id : @duplication,
-  varchar(900) relativePath : string ref,
-  int equivClass : int ref);
+  string relativePath : string ref,
+  int equivClass : int ref
+);
 
 similarCode(
   unique int id : @similarity,
-  varchar(900) relativePath : string ref,
-  int equivClass : int ref);
+  string relativePath : string ref,
+  int equivClass : int ref
+);
 
-@duplication_or_similarity = @duplication | @similarity;
+@duplication_or_similarity = @duplication | @similarity
 
 tokens(
   int id : @duplication_or_similarity ref,
@@ -21,25 +22,35 @@ tokens(
   int beginLine : int ref,
   int beginColumn : int ref,
   int endLine : int ref,
-  int endColumn : int ref);
+  int endColumn : int ref
+);
 
-/** External data **/
+/*- External data -*/
 
+/**
+ * External data, loaded from CSV files during snapshot creation. See
+ * [Tutorial: Incorporating external data](https://help.semmle.com/wiki/display/SD/Tutorial%3A+Incorporating+external+data)
+ * for more information.
+ */
 externalData(
   int id : @externalDataElement,
-  varchar(900) path : string ref,
+  string path : string ref,
   int column: int ref,
-  varchar(900) value : string ref
+  string value : string ref
 );
 
-snapshotDate(unique date snapshotDate : date ref);
+/*- Snapshot date -*/
 
-sourceLocationPrefix(varchar(900) prefix : string ref);
+snapshotDate(unique date snapshotDate : date ref);
 
+/*- Source location prefix -*/
 
-/*
- * XML Files
+/**
+ * The source location of the snapshot.
  */
+sourceLocationPrefix(string prefix : string ref);
+
+/*- XML Files -*/
 
 xmlEncoding(
   unique int id: @file ref,
@@ -110,34 +121,196 @@ xmllocations(
 
 @xmllocatable = @xmlcharacters | @xmlelement | @xmlcomment | @xmlattribute | @xmldtd | @file | @xmlnamespace;
 
-compilations(unique int id: @compilation, string cwd: string ref);
+/*- Compilations -*/
+
+/**
+ * An invocation of the compiler. Note that more than one file may be
+ * compiled per invocation. For example, this command compiles three
+ * source files:
+ *
+ *   gcc -c f1.c f2.c f3.c
+ *
+ * The `id` simply identifies the invocation, while `cwd` is the working
+ * directory from which the compiler was invoked.
+ */
+compilations(
+  /**
+   * An invocation of the compiler. Note that more than one file may
+   * be compiled per invocation. For example, this command compiles
+   * three source files:
+   *
+   *   gcc -c f1.c f2.c f3.c
+   */
+  unique int id : @compilation,
+  string cwd : string ref
+);
 
+/**
+* The arguments that were passed to the extractor for a compiler
+* invocation. If `id` is for the compiler invocation
+*
+*   gcc -c f1.c f2.c f3.c
+*
+* then typically there will be rows for
+*
+* num | arg
+* --- | ---
+* 0   | *path to extractor*
+* 1   | `--mimic`
+* 2   | `/usr/bin/gcc`
+* 3   | `-c`
+* 4   | f1.c
+* 5   | f2.c
+* 6   | f3.c
+*/
 #keyset[id, num]
-compilation_args(int id: @compilation ref, int num: int ref, string arg: string ref);
+compilation_args(
+  int id : @compilation ref,
+  int num : int ref,
+  string arg : string ref
+);
 
+/**
+* The source files that are compiled by a compiler invocation.
+* If `id` is for the compiler invocation
+*
+*   gcc -c f1.c f2.c f3.c
+*
+* then there will be rows for
+*
+* num | arg
+* --- | ---
+* 0   | f1.c
+* 1   | f2.c
+* 2   | f3.c
+*
+* Note that even if those files `#include` headers, those headers
+* do not appear as rows.
+*/
+#keyset[id, num]
+compilation_compiling_files(
+  int id : @compilation ref,
+  int num : int ref,
+  int file : @file ref
+);
+
+/**
+* The time taken by the extractor for a compiler invocation.
+*
+* For each file `num`, there will be rows for
+*
+* kind | seconds
+* ---- | ---
+* 1    | CPU seconds used by the extractor frontend
+* 2    | Elapsed seconds during the extractor frontend
+* 3    | CPU seconds used by the extractor backend
+* 4    | Elapsed seconds during the extractor backend
+*/
 #keyset[id, num, kind]
-compilation_time(int id: @compilation ref, int num: int ref, int kind: int ref, float secs: float ref);
+compilation_time(
+  int id : @compilation ref,
+  int num : int ref,
+  /* kind:
+     1 = frontend_cpu_seconds
+     2 = frontend_elapsed_seconds
+     3 = extractor_cpu_seconds
+     4 = extractor_elapsed_seconds
+  */
+  int kind : int ref,
+  float seconds : float ref
+);
 
-diagnostic_for(unique int diagnostic: @diagnostic ref, int compilation: @compilation ref, int file_number: int ref, int file_number_diagnostic_number: int ref);
+/**
+* An error or warning generated by the extractor.
+* The diagnostic message `diagnostic` was generated during compiler
+* invocation `compilation`, and is the `file_number_diagnostic_number`th
+* message generated while extracting the `file_number`th file of that
+* invocation.
+*/
+#keyset[compilation, file_number, file_number_diagnostic_number]
+diagnostic_for(
+  int diagnostic : @diagnostic ref,
+  int compilation : @compilation ref,
+  int file_number : int ref,
+  int file_number_diagnostic_number : int ref
+);
 
-compilation_finished(unique int id: @compilation ref, float cpu_seconds: float ref, float elapsed_seconds: float ref);
+/**
+* If extraction was successful, then `cpu_seconds` and
+* `elapsed_seconds` are the CPU time and elapsed time (respectively)
+* that extraction took for compiler invocation `id`.
+*/
+compilation_finished(
+  unique int id : @compilation ref,
+  float cpu_seconds : float ref,
+  float elapsed_seconds : float ref
+);
 
-#keyset[id, num]
-compilation_compiling_files(int id: @compilation ref, int num: int ref, int file: @file ref);
+/*- Diagnostic messages -*/
 
-diagnostics(unique int id: @diagnostic, int severity: int ref, string error_tag: string ref, string error_message: string ref,
-            string full_error_message: string ref, int location: @location ref);
+diagnostics(
+  unique int id: @diagnostic,
+  int severity: int ref,
+  string error_tag: string ref,
+  string error_message: string ref,
+  string full_error_message: string ref,
+  int location: @location_default ref
+);
 
-locations_default(unique int id: @location_default, int file: @file ref, int beginLine: int ref, int beginColumn: int ref,
-                  int endLine: int ref, int endColumn: int ref);
+case @diagnostic.severity of
+  10 = @diagnostic_debug
+| 20 = @diagnostic_info
+| 30 = @diagnostic_warning
+| 40 = @diagnostic_error
+;
+
+/*- Files and folders -*/
+
+/**
+ * The location of an element that is not an expression or a statement.
+ * The location spans column `startcolumn` of line `startline` to
+ * column `endcolumn` of line `endline` in file `file`.
+ * For more information, see
+ * [Locations](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
+ */
+locations_default(
+  /** The location of an element that is not an expression or a statement. */
+  unique int id: @location_default,
+  int container: @container ref,
+  int startLine: int ref,
+  int startColumn: int ref,
+  int endLine: int ref,
+  int endColumn: int ref
+);
 
-numlines(int element_id: @sourceline ref, int num_lines: int ref, int num_code: int ref, int num_comment: int ref);
+files(
+  unique int id: @file,
+  string name: string ref
+);
 
-files(unique int id: @file, string name: string ref);
+folders(
+  unique int id: @folder,
+  string name: string ref
+);
+
+@container = @file | @folder
 
-folders(unique int id: @folder, string name: string ref);
+containerparent(
+  int parent: @container ref,
+  unique int child: @container ref
+);
 
-containerparent(int parent: @container ref, unique int child: @container ref);
+/*- Lines of code -*/
+
+#keyset[element_id]
+numlines(
+  int element_id: @sourceline ref,
+  int num_lines: int ref,
+  int num_code: int ref,
+  int num_comment: int ref
+);
+
+/*- GO-specific part -*/
 
 has_location(unique int locatable: @locatable ref, int location: @location ref);
 
@@ -231,8 +404,6 @@ variadic(int id: @signaturetype ref);
 typeparam(unique int tp: @typeparamtype ref, string name: string ref, int bound: @compositetype ref,
           int parent: @typeparamparentobject ref, int idx: int ref);
 
-@container = @file | @folder;
-
 @locatable = @xmllocatable | @node | @localscope;
 
 @node = @documentable | @exprparent | @modexprparent | @fieldparent | @stmtparent | @declparent | @typeparamdeclparent
diff --git a/java/ql/lib/config/semmlecode.dbscheme b/java/ql/lib/config/semmlecode.dbscheme
index 7cbc85b1f3ec..67f6c5c0644c 100644
--- a/java/ql/lib/config/semmlecode.dbscheme
+++ b/java/ql/lib/config/semmlecode.dbscheme
@@ -1,3 +1,4 @@
+/*- Compilations (Java) -*/
 /**
  * An invocation of the compiler. Note that more than one file may be
  * compiled per invocation. For example, this command compiles three
@@ -181,20 +182,32 @@ compilation_finished(
     int result : int ref
 );
 
+/*- Diagnostic messages -*/
+
 diagnostics(
-    unique int id: @diagnostic,
-    string generated_by: string ref, // TODO: Sync this with the other languages?
-    int severity: int ref,
-    string error_tag: string ref,
-    string error_message: string ref,
-    string full_error_message: string ref,
-    int location: @location_default ref
+  unique int id: @diagnostic,
+  string generated_by: string ref, // TODO: Sync this with the other languages?
+  int severity: int ref,
+  string error_tag: string ref,
+  string error_message: string ref,
+  string full_error_message: string ref,
+  int location: @location_default ref
 );
 
-/*
- * External artifacts
- */
+case @diagnostic.severity of
+  10 = @diagnostic_debug
+| 20 = @diagnostic_info
+| 30 = @diagnostic_warning
+| 40 = @diagnostic_error
+;
+
+/*- External data -*/
 
+/**
+ * External data, loaded from CSV files during snapshot creation. See
+ * [Tutorial: Incorporating external data](https://help.semmle.com/wiki/display/SD/Tutorial%3A+Incorporating+external+data)
+ * for more information.
+ */
 externalData(
   int id : @externalDataElement,
   string path : string ref,
@@ -202,17 +215,18 @@ externalData(
   string value : string ref
 );
 
-snapshotDate(
-  unique date snapshotDate : date ref
-);
+/*- Snapshot date -*/
 
-sourceLocationPrefix(
-  string prefix : string ref
-);
+snapshotDate(unique date snapshotDate : date ref);
 
-/*
- * Duplicate code
+/*- Source location prefix -*/
+
+/**
+ * The source location of the snapshot.
  */
+sourceLocationPrefix(string prefix : string ref);
+
+/*- Duplicate code -*/
 
 duplicateCode(
   unique int id : @duplication,
@@ -237,6 +251,8 @@ tokens(
   int endColumn : int ref
 );
 
+/*- SMAP -*/
+
 /*
  * SMAP
  */
@@ -265,36 +281,25 @@ smap_lines(
   int outputLineIncrement: int ref
 );
 
-/*
- * Locations and files
- */
-
-@location = @location_default ;
+/*- Files and folders -*/
 
+/**
+ * The location of an element that is not an expression or a statement.
+ * The location spans column `startcolumn` of line `startline` to
+ * column `endcolumn` of line `endline` in file `file`.
+ * For more information, see
+ * [Locations](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
+ */
 locations_default(
+  /** The location of an element that is not an expression or a statement. */
   unique int id: @location_default,
-  int file: @file ref,
-  int beginLine: int ref,
-  int beginColumn: int ref,
+  int container: @container ref,
+  int startLine: int ref,
+  int startColumn: int ref,
   int endLine: int ref,
   int endColumn: int ref
 );
 
-hasLocation(
-  int locatableid: @locatable ref,
-  int id: @location ref
-);
-
-@sourceline = @locatable ;
-
-#keyset[element_id]
-numlines(
-  int element_id: @sourceline ref,
-  int num_lines: int ref,
-  int num_code: int ref,
-  int num_comment: int ref
-);
-
 files(
   unique int id: @file,
   string name: string ref
@@ -305,16 +310,33 @@ folders(
   string name: string ref
 );
 
-@container = @folder | @file
+@container = @file | @folder
 
 containerparent(
   int parent: @container ref,
   unique int child: @container ref
 );
 
-/*
- * Java
- */
+/*- Lines of code -*/
+
+#keyset[element_id]
+numlines(
+  int element_id: @sourceline ref,
+  int num_lines: int ref,
+  int num_code: int ref,
+  int num_comment: int ref
+);
+
+/*- Java -*/
+
+@location = @location_default ;
+
+hasLocation(
+  int locatableid: @locatable ref,
+  int id: @location ref
+);
+
+@sourceline = @locatable ;
 
 cupackage(
   unique int id: @file ref,
@@ -1060,9 +1082,7 @@ javadocText(
 
 @top = @element | @locatable | @folder;
 
-/*
- * XML Files
- */
+/*- XML Files -*/
 
 xmlEncoding(
   unique int id: @file ref,
@@ -1133,9 +1153,7 @@ xmllocations(
 
 @xmllocatable = @xmlcharacters | @xmlelement | @xmlcomment | @xmlattribute | @xmldtd | @file | @xmlnamespace;
 
-/*
- * configuration files with key value pairs
- */
+/*- configuration files with key value pairs -*/
 
 configs(
   unique int id: @config
@@ -1160,6 +1178,8 @@ configLocations(
 
 @configLocatable = @config | @configName | @configValue;
 
+/*- Kotlin -*/
+
 ktComments(
   unique int id: @ktcomment,
   int kind: int ref,
diff --git a/javascript/ql/lib/semmlecode.javascript.dbscheme b/javascript/ql/lib/semmlecode.javascript.dbscheme
index 4d00210ca570..df77779bec97 100644
--- a/javascript/ql/lib/semmlecode.javascript.dbscheme
+++ b/javascript/ql/lib/semmlecode.javascript.dbscheme
@@ -1,51 +1,66 @@
 /*** Standard fragments ***/
 
-/** Files and folders **/
+/*- Files and folders -*/
 
-@location = @location_default;
-
-locations_default(unique int id: @location_default,
-          int file: @file ref,
-          int beginLine: int ref,
-          int beginColumn: int ref,
-          int endLine: int ref,
-          int endColumn: int ref
-         );
-
-@sourceline = @locatable;
-
-numlines(int element_id: @sourceline ref,
-         int num_lines: int ref,
-         int num_code: int ref,
-         int num_comment: int ref
-        );
+/**
+ * The location of an element that is not an expression or a statement.
+ * The location spans column `startcolumn` of line `startline` to
+ * column `endcolumn` of line `endline` in file `file`.
+ * For more information, see
+ * [Locations](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
+ */
+locations_default(
+  /** The location of an element that is not an expression or a statement. */
+  unique int id: @location_default,
+  int container: @container ref,
+  int startLine: int ref,
+  int startColumn: int ref,
+  int endLine: int ref,
+  int endColumn: int ref
+);
 
-files(unique int id: @file,
-      varchar(900) name: string ref);
+files(
+  unique int id: @file,
+  string name: string ref
+);
 
-folders(unique int id: @folder,
-        varchar(900) name: string ref);
+folders(
+  unique int id: @folder,
+  string name: string ref
+);
 
+@container = @file | @folder
 
-@container = @folder | @file ;
+containerparent(
+  int parent: @container ref,
+  unique int child: @container ref
+);
 
+/*- Lines of code -*/
 
-containerparent(int parent: @container ref,
-                unique int child: @container ref);
+#keyset[element_id]
+numlines(
+  int element_id: @sourceline ref,
+  int num_lines: int ref,
+  int num_code: int ref,
+  int num_comment: int ref
+);
 
-/** Duplicate code **/
+/*- Duplicate code -*/
 
 duplicateCode(
   unique int id : @duplication,
-  varchar(900) relativePath : string ref,
-  int equivClass : int ref);
+  string relativePath : string ref,
+  int equivClass : int ref
+);
 
 similarCode(
   unique int id : @similarity,
-  varchar(900) relativePath : string ref,
-  int equivClass : int ref);
+  string relativePath : string ref,
+  int equivClass : int ref
+);
 
-@duplication_or_similarity = @duplication | @similarity;
+@duplication_or_similarity = @duplication | @similarity
 
 tokens(
   int id : @duplication_or_similarity ref,
@@ -53,51 +68,67 @@ tokens(
   int beginLine : int ref,
   int beginColumn : int ref,
   int endLine : int ref,
-  int endColumn : int ref);
+  int endColumn : int ref
+);
 
-/** External data **/
+/*- External data -*/
 
+/**
+ * External data, loaded from CSV files during snapshot creation. See
+ * [Tutorial: Incorporating external data](https://help.semmle.com/wiki/display/SD/Tutorial%3A+Incorporating+external+data)
+ * for more information.
+ */
 externalData(
   int id : @externalDataElement,
-  varchar(900) path : string ref,
+  string path : string ref,
   int column: int ref,
-  varchar(900) value : string ref
+  string value : string ref
 );
 
+/*- Snapshot date -*/
+
 snapshotDate(unique date snapshotDate : date ref);
 
-sourceLocationPrefix(varchar(900) prefix : string ref);
+/*- Source location prefix -*/
 
-/** Version control data **/
+/**
+ * The source location of the snapshot.
+ */
+sourceLocationPrefix(string prefix : string ref);
+
+/*- Version control data -*/
 
 svnentries(
-  int id : @svnentry,
-  varchar(500) revision : string ref,
-  varchar(500) author : string ref,
+  unique int id : @svnentry,
+  string revision : string ref,
+  string author : string ref,
   date revisionDate : date ref,
   int changeSize : int ref
-);
+)
 
 svnaffectedfiles(
   int id : @svnentry ref,
   int file : @file ref,
-  varchar(500) action : string ref
-);
+  string action : string ref
+)
 
 svnentrymsg(
-  int id : @svnentry ref,
-  varchar(500) message : string ref
-);
+  unique int id : @svnentry ref,
+  string message : string ref
+)
 
 svnchurn(
   int commit : @svnentry ref,
   int file : @file ref,
   int addedLines : int ref,
   int deletedLines : int ref
-);
+)
 
+/*- JavaScript-specific part -*/
 
-/*** JavaScript-specific part ***/
+@location = @location_default
+
+@sourceline = @locatable;
 
 filetype(
   int file: @file ref,
@@ -1046,7 +1077,43 @@ jsdoc_has_new_parameter (int fn: @jsdoc_function_type_expr ref);
 
 jsdoc_errors (unique int id: @jsdoc_error, int tag: @jsdoc_tag ref, varchar(900) message: string ref, varchar(900) tostring: string ref);
 
-// YAML
+@dataflownode = @expr | @function_decl_stmt | @class_decl_stmt | @namespace_declaration | @enum_declaration | @property;
+
+@optionalchainable = @call_expr | @propaccess;
+
+isOptionalChaining(int id: @optionalchainable ref);
+
+/**
+ * The time taken for the extraction of a file.
+ * This table contains non-deterministic content.
+ *
+ * The sum of the `time` column for each (`file`, `timerKind`) pair
+ * is the total time taken for extraction of `file`.  The `extractionPhase`
+ * column provides a granular view of the extraction time of the file.
+ */
+extraction_time(
+  int file : @file ref,
+  // see `com.semmle.js.extractor.ExtractionMetrics.ExtractionPhase`.
+  int extractionPhase: int ref,
+  // 0 for the elapsed CPU time in nanoseconds, 1 for the elapsed wallclock time in nanoseconds
+  int timerKind: int ref,
+  float time: float ref
+)
+
+/**
+* Non-timing related data for the extraction of a single file.
+* This table contains non-deterministic content.
+*/
+extraction_data(
+  int file : @file ref,
+  // the absolute path to the cache file
+  varchar(900) cacheFile: string ref,
+  boolean fromCache: boolean ref,
+  int length: int ref
+)
+
+/*- YAML -*/
+
 #keyset[parent, idx]
 yaml (unique int id: @yaml_node,
       int kind: int ref,
@@ -1084,24 +1151,24 @@ yaml_locations(unique int locatable: @yaml_locatable ref,
 
 @yaml_locatable = @yaml_node | @yaml_error;
 
-/* XML Files */
+/*- XML Files -*/
 
 xmlEncoding(
   unique int id: @file ref,
-  varchar(900) encoding: string ref
+  string encoding: string ref
 );
 
 xmlDTDs(
   unique int id: @xmldtd,
-  varchar(900) root: string ref,
-  varchar(900) publicId: string ref,
-  varchar(900) systemId: string ref,
+  string root: string ref,
+  string publicId: string ref,
+  string systemId: string ref,
   int fileid: @file ref
 );
 
 xmlElements(
   unique int id: @xmlelement,
-  varchar(900) name: string ref,
+  string name: string ref,
   int parentid: @xmlparent ref,
   int idx: int ref,
   int fileid: @file ref
@@ -1110,16 +1177,16 @@ xmlElements(
 xmlAttrs(
   unique int id: @xmlattribute,
   int elementid: @xmlelement ref,
-  varchar(900) name: string ref,
-  varchar(3600) value: string ref,
+  string name: string ref,
+  string value: string ref,
   int idx: int ref,
   int fileid: @file ref
 );
 
 xmlNs(
   int id: @xmlnamespace,
-  varchar(900) prefixName: string ref,
-  varchar(900) URI: string ref,
+  string prefixName: string ref,
+  string URI: string ref,
   int fileid: @file ref
 );
 
@@ -1131,14 +1198,14 @@ xmlHasNs(
 
 xmlComments(
   unique int id: @xmlcomment,
-  varchar(3600) text: string ref,
+  string text: string ref,
   int parentid: @xmlparent ref,
   int fileid: @file ref
 );
 
 xmlChars(
   unique int id: @xmlcharacters,
-  varchar(3600) text: string ref,
+  string text: string ref,
   int parentid: @xmlparent ref,
   int idx: int ref,
   int isCDATA: int ref,
@@ -1155,15 +1222,7 @@ xmllocations(
 
 @xmllocatable = @xmlcharacters | @xmlelement | @xmlcomment | @xmlattribute | @xmldtd | @file | @xmlnamespace;
 
-@dataflownode = @expr | @function_decl_stmt | @class_decl_stmt | @namespace_declaration | @enum_declaration | @property;
-
-@optionalchainable = @call_expr | @propaccess;
-
-isOptionalChaining(int id: @optionalchainable ref);
-
-/*
- * configuration files with key value pairs
- */
+/*- configuration files with key value pairs -*/
 
 configs(
   unique int id: @config
@@ -1188,31 +1247,3 @@ configLocations(
 
 @configLocatable = @config | @configName | @configValue;
 
-/**
- * The time taken for the extraction of a file.
- * This table contains non-deterministic content.
- *
- * The sum of the `time` column for each (`file`, `timerKind`) pair
- * is the total time taken for extraction of `file`.  The `extractionPhase`
- * column provides a granular view of the extraction time of the file.
- */
-extraction_time(
-   int file : @file ref,
-   // see `com.semmle.js.extractor.ExtractionMetrics.ExtractionPhase`.
-   int extractionPhase: int ref,
-   // 0 for the elapsed CPU time in nanoseconds, 1 for the elapsed wallclock time in nanoseconds
-   int timerKind: int ref,
-   float time: float ref
-)
-
-/**
- * Non-timing related data for the extraction of a single file.
- * This table contains non-deterministic content.
- */
-extraction_data(
-   int file : @file ref,
-   // the absolute path to the cache file
-   varchar(900) cacheFile: string ref,
-   boolean fromCache: boolean ref,
-   int length: int ref
-)
diff --git a/python/ql/lib/semmlecode.python.dbscheme b/python/ql/lib/semmlecode.python.dbscheme
index 47e552c4357a..8b0d2fe30b7c 100644
--- a/python/ql/lib/semmlecode.python.dbscheme
+++ b/python/ql/lib/semmlecode.python.dbscheme
@@ -16,9 +16,7 @@
  * mechanism not work properly.
  */
 
- /*
- * External artifacts
- */
+/*- External defects and metrics -*/
 
 externalDefects(
   unique int id : @externalDefect,
@@ -35,31 +33,44 @@ externalMetrics(
   float value : float ref
 );
 
+/*- External data -*/
+
+/**
+ * External data, loaded from CSV files during snapshot creation. See
+ * [Tutorial: Incorporating external data](https://help.semmle.com/wiki/display/SD/Tutorial%3A+Incorporating+external+data)
+ * for more information.
+ */
 externalData(
   int id : @externalDataElement,
-  varchar(900) queryPath : string ref,
+  string path : string ref,
   int column: int ref,
-  varchar(900) data : string ref
+  string value : string ref
 );
 
-snapshotDate(unique date snapshotDate : date ref);
+/*- Snapshot date -*/
 
-sourceLocationPrefix(varchar(900) prefix : string ref);
+snapshotDate(unique date snapshotDate : date ref);
 
+/*- Source location prefix -*/
 
-/*
- * Duplicate code
+/**
+ * The source location of the snapshot.
  */
+sourceLocationPrefix(string prefix : string ref);
+
+/*- Duplicate code -*/
 
 duplicateCode(
   unique int id : @duplication,
-  varchar(900) relativePath : string ref,
-  int equivClass : int ref);
+  string relativePath : string ref,
+  int equivClass : int ref
+);
 
 similarCode(
   unique int id : @similarity,
-  varchar(900) relativePath : string ref,
-  int equivClass : int ref);
+  string relativePath : string ref,
+  int equivClass : int ref
+);
 
 @duplication_or_similarity = @duplication | @similarity
 
@@ -69,31 +80,15 @@ tokens(
   int beginLine : int ref,
   int beginColumn : int ref,
   int endLine : int ref,
-  int endColumn : int ref);
-
-/*
- * Line metrics
- */
-py_codelines(int id : @py_scope ref,
-             int count : int ref);
-
-py_commentlines(int id : @py_scope ref,
-                int count : int ref);
-
-py_docstringlines(int id : @py_scope ref,
-                int count : int ref);
+  int endColumn : int ref
+);
 
-py_alllines(int id : @py_scope ref,
-                int count : int ref);
-
-/*
- * Version history
- */
+/*- Version control data -*/
 
 svnentries(
-  int id : @svnentry,
-  varchar(500) revision : string ref,
-  varchar(500) author : string ref,
+  unique int id : @svnentry,
+  string revision : string ref,
+  string author : string ref,
   date revisionDate : date ref,
   int changeSize : int ref
 )
@@ -101,12 +96,12 @@ svnentries(
 svnaffectedfiles(
   int id : @svnentry ref,
   int file : @file ref,
-  varchar(500) action : string ref
+  string action : string ref
 )
 
 svnentrymsg(
-  int id : @svnentry ref,
-  varchar(500) message : string ref
+  unique int id : @svnentry ref,
+  string message : string ref
 )
 
 svnchurn(
@@ -116,37 +111,72 @@ svnchurn(
   int deletedLines : int ref
 )
 
-/****************************
-        Python dbscheme
-****************************/
+/*- Lines of code -*/
 
-files(unique int id: @file,
-      varchar(900) name: string ref);
+#keyset[element_id]
+numlines(
+  int element_id: @sourceline ref,
+  int num_lines: int ref,
+  int num_code: int ref,
+  int num_comment: int ref
+);
 
-folders(unique int id: @folder,
-        varchar(900) name: string ref);
+/*- Files and folders -*/
 
-@container = @folder | @file;
+/**
+ * The location of an element that is not an expression or a statement.
+ * The location spans column `startcolumn` of line `startline` to
+ * column `endcolumn` of line `endline` in file `file`.
+ * For more information, see
+ * [Locations](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
+ */
+locations_default(
+  /** The location of an element that is not an expression or a statement. */
+  unique int id: @location_default,
+  int container: @container ref,
+  int startLine: int ref,
+  int startColumn: int ref,
+  int endLine: int ref,
+  int endColumn: int ref
+);
 
-containerparent(int parent: @container ref,
-                unique int child: @container ref);
+files(
+  unique int id: @file,
+  string name: string ref
+);
 
-@sourceline = @file | @py_Module | @xmllocatable;
+folders(
+  unique int id: @folder,
+  string name: string ref
+);
 
-numlines(int element_id: @sourceline ref,
-         int num_lines: int ref,
-         int num_code: int ref,
-         int num_comment: int ref
-        );
+@container = @file | @folder
 
-@location = @location_ast | @location_default ;
+containerparent(
+  int parent: @container ref,
+  unique int child: @container ref
+);
 
-locations_default(unique int id: @location_default,
-          int file: @file ref,
-          int beginLine: int ref,
-          int beginColumn: int ref,
-          int endLine: int ref,
-          int endColumn: int ref);
+/*- Python dbscheme -*/
+
+/*
+ * Line metrics
+ */
+py_codelines(int id : @py_scope ref,
+    int count : int ref);
+
+py_commentlines(int id : @py_scope ref,
+       int count : int ref);
+
+py_docstringlines(int id : @py_scope ref,
+       int count : int ref);
+
+py_alllines(int id : @py_scope ref,
+       int count : int ref);
+
+@sourceline = @file | @py_Module | @xmllocatable;
+
+@location = @location_ast | @location_default ;
 
 locations_ast(unique int id: @location_ast,
           int module: @py_Module ref,
@@ -1053,54 +1083,74 @@ py_decorated_object(int object : @py_object ref,
 
 @py_source_element = @py_ast_node | @container;
 
-/* XML Files */
-
-xmlEncoding  (unique int id: @file ref, varchar(900) encoding: string ref);
-
-xmlDTDs       (unique int id: @xmldtd,
-              varchar(900) root: string ref,
-              varchar(900) publicId: string ref,
-              varchar(900) systemId: string ref,
-              int fileid: @file ref);
-
-xmlElements   (unique int id: @xmlelement,
-              varchar(900) name: string ref,
-              int parentid: @xmlparent ref,
-              int idx: int ref,
-              int fileid: @file ref);
-
-xmlAttrs      (unique int id: @xmlattribute,
-              int elementid: @xmlelement ref,
-              varchar(900) name: string ref,
-              varchar(3600) value: string ref,
-              int idx: int ref,
-              int fileid: @file ref);
-
-xmlNs         (int id: @xmlnamespace,
-              varchar(900) prefixName: string ref,
-              varchar(900) URI: string ref,
-              int fileid: @file ref);
-
-xmlHasNs      (int elementId: @xmlnamespaceable ref,
-              int nsId: @xmlnamespace ref,
-              int fileid: @file ref);
-
-xmlComments   (unique int id: @xmlcomment,
-              varchar(3600) text: string ref,
-              int parentid: @xmlparent ref,
-              int fileid: @file ref);
-
-xmlChars      (unique int id: @xmlcharacters,
-              varchar(3600) text: string ref,
-              int parentid: @xmlparent ref,
-              int idx: int ref,
-              int isCDATA: int ref,
-              int fileid: @file ref);
+/*- XML Files -*/
+
+xmlEncoding(
+  unique int id: @file ref,
+  string encoding: string ref
+);
+
+xmlDTDs(
+  unique int id: @xmldtd,
+  string root: string ref,
+  string publicId: string ref,
+  string systemId: string ref,
+  int fileid: @file ref
+);
+
+xmlElements(
+  unique int id: @xmlelement,
+  string name: string ref,
+  int parentid: @xmlparent ref,
+  int idx: int ref,
+  int fileid: @file ref
+);
+
+xmlAttrs(
+  unique int id: @xmlattribute,
+  int elementid: @xmlelement ref,
+  string name: string ref,
+  string value: string ref,
+  int idx: int ref,
+  int fileid: @file ref
+);
+
+xmlNs(
+  int id: @xmlnamespace,
+  string prefixName: string ref,
+  string URI: string ref,
+  int fileid: @file ref
+);
+
+xmlHasNs(
+  int elementId: @xmlnamespaceable ref,
+  int nsId: @xmlnamespace ref,
+  int fileid: @file ref
+);
+
+xmlComments(
+  unique int id: @xmlcomment,
+  string text: string ref,
+  int parentid: @xmlparent ref,
+  int fileid: @file ref
+);
+
+xmlChars(
+  unique int id: @xmlcharacters,
+  string text: string ref,
+  int parentid: @xmlparent ref,
+  int idx: int ref,
+  int isCDATA: int ref,
+  int fileid: @file ref
+);
 
 @xmlparent = @file | @xmlelement;
 @xmlnamespaceable = @xmlelement | @xmlattribute;
 
-xmllocations(int xmlElement: @xmllocatable ref,
-             int location: @location_default ref);
+xmllocations(
+  int xmlElement: @xmllocatable ref,
+  int location: @location_default ref
+);
 
 @xmllocatable = @xmlcharacters | @xmlelement | @xmlcomment | @xmlattribute | @xmldtd | @file | @xmlnamespace;
+
diff --git a/ql/ql/src/ql.dbscheme b/ql/ql/src/ql.dbscheme
index 2f4f6f7d26ff..47a06637005e 100644
--- a/ql/ql/src/ql.dbscheme
+++ b/ql/ql/src/ql.dbscheme
@@ -1,15 +1,23 @@
 // CodeQL database schema for QL
 // Automatically generated from the tree-sitter grammar; do not edit
 
-@location = @location_default
-
+/*- Files and folders -*/
+
+/**
+ * The location of an element that is not an expression or a statement.
+ * The location spans column `startcolumn` of line `startline` to
+ * column `endcolumn` of line `endline` in file `file`.
+ * For more information, see
+ * [Locations](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
+ */
 locations_default(
+  /** The location of an element that is not an expression or a statement. */
   unique int id: @location_default,
-  int file: @file ref,
-  int start_line: int ref,
-  int start_column: int ref,
-  int end_line: int ref,
-  int end_column: int ref
+  int container: @container ref,
+  int startLine: int ref,
+  int startColumn: int ref,
+  int endLine: int ref,
+  int endColumn: int ref
 );
 
 files(
@@ -29,9 +37,14 @@ containerparent(
   unique int child: @container ref
 );
 
-sourceLocationPrefix(
-  string prefix: string ref
-);
+/*- Source location prefix -*/
+
+/**
+ * The source location of the snapshot.
+ */
+sourceLocationPrefix(string prefix : string ref);
+
+/*- Diagnostic messages -*/
 
 diagnostics(
   unique int id: @diagnostic,
@@ -49,6 +62,9 @@ case @diagnostic.severity of
 | 40 = @diagnostic_error
 ;
 
+/*- QL-specific part -*/
+
+@location = @location_default
 
 @ql_add_expr_left_type = @ql_add_expr | @ql_aggregate | @ql_call_or_unqual_agg_expr | @ql_comp_term | @ql_conjunction | @ql_disjunction | @ql_expr_annotation | @ql_if_term | @ql_implication | @ql_in_expr | @ql_instance_of | @ql_literal | @ql_mul_expr | @ql_negation | @ql_par_expr | @ql_prefix_cast | @ql_qualified_expr | @ql_quantified | @ql_range | @ql_set_literal | @ql_special_call | @ql_super_ref | @ql_unary_expr | @ql_variable
 
diff --git a/ruby/ql/lib/ruby.dbscheme b/ruby/ql/lib/ruby.dbscheme
index ff289788b155..3588c314cc48 100644
--- a/ruby/ql/lib/ruby.dbscheme
+++ b/ruby/ql/lib/ruby.dbscheme
@@ -1,15 +1,23 @@
 // CodeQL database schema for Ruby
 // Automatically generated from the tree-sitter grammar; do not edit
 
-@location = @location_default
-
+/*- Files and folders -*/
+
+/**
+ * The location of an element that is not an expression or a statement.
+ * The location spans column `startcolumn` of line `startline` to
+ * column `endcolumn` of line `endline` in file `file`.
+ * For more information, see
+ * [Locations](https://codeql.github.com/docs/writing-codeql-queries/providing-locations-in-codeql-queries/).
+ */
 locations_default(
+  /** The location of an element that is not an expression or a statement. */
   unique int id: @location_default,
-  int file: @file ref,
-  int start_line: int ref,
-  int start_column: int ref,
-  int end_line: int ref,
-  int end_column: int ref
+  int container: @container ref,
+  int startLine: int ref,
+  int startColumn: int ref,
+  int endLine: int ref,
+  int endColumn: int ref
 );
 
 files(
@@ -29,9 +37,14 @@ containerparent(
   unique int child: @container ref
 );
 
-sourceLocationPrefix(
-  string prefix: string ref
-);
+/*- Source location prefix -*/
+
+/**
+ * The source location of the snapshot.
+ */
+sourceLocationPrefix(string prefix : string ref);
+
+/*- Diagnostic messages -*/
 
 diagnostics(
   unique int id: @diagnostic,
@@ -49,6 +62,9 @@ case @diagnostic.severity of
 | 40 = @diagnostic_error
 ;
 
+/*- Ruby-specific part -*/
+
+@location = @location_default
 
 @ruby_underscore_arg = @ruby_assignment | @ruby_binary | @ruby_conditional | @ruby_operator_assignment | @ruby_range | @ruby_unary | @ruby_underscore_primary
 
@@ -1378,6 +1394,8 @@ ruby_ast_node_info(
   int loc: @location ref
 );
 
+/*- ERB-specific part -*/
+
 erb_comment_directive_child(
   unique int erb_comment_directive: @erb_comment_directive ref,
   unique int child: @erb_token_comment ref
diff --git a/swift/prefix.dbscheme b/swift/prefix.dbscheme
index b422464bb902..04c524176d90 100644
--- a/swift/prefix.dbscheme
+++ b/swift/prefix.dbscheme
@@ -1,6 +1,7 @@
+/*- Source location prefix -*/
+
 /**
  * The source location of the snapshot.
  */
-sourceLocationPrefix(
-  string prefix: string ref
-);
+sourceLocationPrefix(string prefix : string ref);
+
diff --git a/swift/ql/lib/swift.dbscheme b/swift/ql/lib/swift.dbscheme
index e457bc35325b..d3b2b010500e 100644
--- a/swift/ql/lib/swift.dbscheme
+++ b/swift/ql/lib/swift.dbscheme
@@ -1,14 +1,11 @@
-// generated by codegen/codegen.py
+/*- Source location prefix -*/
 
-// from prefix.dbscheme
 /**
  * The source location of the snapshot.
  */
-sourceLocationPrefix(
-  string prefix: string ref
-);
-
+sourceLocationPrefix(string prefix : string ref);
 
+/*- Swift-specific part -*/
 // from schema.py
 
 @element =