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FIX SBE XML Primer

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Todd L. Montgomery edited this page Nov 15, 2013 · 23 revisions

FIX/SBE uses an XML format to specify messages, headers, and other elements. The system is typed and users can create new types from primitives. In this section, we will discuss the practical aspects of the XML specification. For details, please see the FIX/SBE specification. An example schema can be found here.

messageSchema Element

The messageSchema element is the root document in XML. It contains primarily all types and messages specified. This element has the following fields:

  • package: Package. This is the namespace for C++ and package name for Java.
  • version: Version number of the attached messages and types. Defaults to 0.
  • semanticVersion: Semantic version information as a string.
  • description: Description of the entire message schema. (optional)
  • byteOrder: The default byte ordering (bigEndian or littleEndian) for all messages types. Default is littleEndian.

An example messageSchema element would be:

<messageSchema package="uk.co.real_logic.sbe.examples"
               semanticVersion="5.2"
               description="Code generation unit test support"
               byteOrder="littleEndian">

A messageSchema holds two main components. types and a list of message elements.

types Element

The types block holds various created types, bit sets, enumerations, and composites.

Primitive Types

All encoding and decoding for SBE is centered around a set of basic primitive types. These are the primitive types.

  • char: Signed character. 8 bits.
  • int8: Signed 8-bit encoding.
  • int16: Signed 16-bit encoding.
  • int32: Signed 32-bit encoding.
  • int64: Signed 64-bit encoding.
  • uint8: Unsigned 8-bit encoding.
  • uint16: Unsigned 16-bit encoding.
  • uint32: Unsigned 32-bit encoding.
  • uint64: Unsigned 64-bit encoding.
  • float: 32-bit floating point encoding. IEEE 754.
  • double: 64-bit floating point encoding. IEEE 754.

type Element

Types can be created by name and by composing a set of builtin primitive types. The type element has the following attributes.

  • name: Name of the type.
  • presence: One of constant, required, or optional. Default is required.
  • semanticType: Semantic information about the type. (optional)
  • description: Description of the type. (optional)
  • primitiveType: Primitive Type of the type.
  • length: Length in primitive type units of the type. Default is 1.
  • characterEncoding: Character Encoding of the type.

An few examples of the use of type are below:

<type name="ModelYear" primitiveType="uint16" semanticType="ModelYear"/>
<type name="VehicleCode" primitiveType="char" length="6" semanticType="VehicleCode"/>
<type name="someNumbers" primitiveType="int32" length="5" semanticType="SomeArray"/>
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