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DataDefinition and its datamodel

Introduction

The DDL (Data Definition Language) was introduced with the software ADTF (Automotive Data- and Time-Triggered Framework) developed and deployed by AUDI AG/VW Group since many years.

The intension was to have a common dynamic description for byte positions and value types for any structured data and memory blocks. Since the software was designed for C++ applications the DDL is similar to it and uses there data types by default.

Example

DDL description for data of following struct:

 struct MyData // => usually aligned size to 4 in c++ because value_3 is aligned to 4
 {
      uint8_t  value_1; // => usually aligned to 1 in c++
      uint16_t value_2; // => usually aligned to 2 in c++
      uint8_t  value_3; // => usually aligned to 1 in c++
      uint32_t value_3; // => usually aligned to 4 in c++
 };

Description in DDL 4.1 as is (in XML):

  • use of default alignments and byteorders
  • use of default byteorder "little endianess"
<struct name="MyData12Byte" alignment="4">
     <element name="value_1" type="uint8_t">
        <serialized bytepos="0" byteorder="LE"/>
        <deserialzed alignment="1"/>
     </element>
     <element name="value_2" type="uint16_t">     
        <serialized bytepos="1" byteorder="LE"/>
        <deserialzed alignment="2"/>
     </element>
     <element name="value_3" type="uint8_t">
        <serialized bytepos="3" byteorder="LE"/>
        <deserialzed alignment="1"/>
     </element>
     <element name="value_4" type="uint32_t">
        <serialized bytepos="4" byteorder="LE"/>
        <deserialzed alignment="4"/>
     </element>
</struct>
deserialized representation(12 bytes in memory)
byte 0 byte 1 byte 2 byte 3 byte 4 byte 5 byte 6 byte 7 byte 8 byte 9 byte 10 byte 11
uint8_t value_1 (padding) uint16_t value_2 uint8_t value_3 (padding) uint32_t value_4
serialized representation (8 bytes in network or file)
byte 0 byte 1 byte 2 byte 3 byte 4 byte 5 byte 6 byte 7
uint8_t value_1 uint16_t value_2 uint8_t value_3 uint32_t value_4

The DDL Library

To facilitate the handling of DDL hierarchies there is a datamodel provided (ddl::dd::datamodel::DataDefinition). This datamodel is validated by a ddl::dd::DataDefinition which keeps the datamodel clean and well-formed.

The datamodel itself and its specification is described within DDL - XML Datamodel specification.

Use the datamodel to handle the model by yourself. We recommend to use following DataDefinition creation API.

DataDefinition creation API

There are 3 ways to create a valid DataDefinition.

Create a file or read it

  • See ddl::DDFile

Create a string or read it

  • See ddl::DDString

Create a DataDefinition via DDStructure or "type reflection"

  • See ddl::DDStructure
  • See ddl::DDStructureGenerator

Binary model classes

DDL Tag/Attribute DDL Class
<ddl:ddl> ddl::dd::DataDefinition
<header> ddl::dd::Header
<baseunit> ddl::dd::BaseUnit
<prefix> ddl::dd::UnitPrefix
<unit> ddl::dd::Unit
<datatype> ddl::dd::DataType
<enum> ddl::dd::EnumType
<struct> ddl::dd::StructType
<streammetatype> ddl::dd::StreamMetaType
<stream> ddl::dd::Stream