ISO 10303-21:2016(E)
The data sections contain instances to be transferred by the exchange structure. Each data section contains instances of entities that correspond to one EXPRESS schema specified in the header section.
The syntax of the data section is prescribed in Table 3. Each data section shall begin with the "DATA" keyword. If an exchange structure contains more than one data section, each "DATA" keyword shall be followed by a parenthesized PARAMETER_LIST containing a STRING and a LIST parameter.
The first parameter shall be a STRING containing a unique name for the section. The second parameter shall be a LIST containing exactly one STRING. The string shall be the name of the schema that shall govern the data section. The schema name must appear in the header section file_schema entry.
If an exchange structure contains only one data section, the parenthesized PARAMETER_LIST may be omitted. In this case, the header section file_schema entry shall specify only one schema, and that schema shall govern the data section.
Each data section shall be terminated with the special token "ENDSEC;".
NOTE 1 The data section is optional in this edition of this part of ISO 10303 so that exchange structures may be created for the purpose of defining forwarding references to other structures
NOTE 2 Annexes H and I present complete examples of a data section within an exchange structure.
Each entity instance that is not defined by an external reference (see clause 10) shall be mapped to an ENTITY_INSTANCE (see Table 3) in the data section, as specified in 12.2. Each entity instance shall be represented at most once in the exchange structure and shall have an instance name that is unique within the exchange structure. The entity instances need not be ordered in the exchange structure. An instance name may be referenced before it is defined.
A user-defined entity instance is an entity that is not part of the EXPRESS schema specified in the header section. User-defined entity instances shall conform to the same syntax of all data section entity instances except that the USER_DEFINED_KEYWORD choice shall be used in the SIMPLE_RECORD that is part of this definition. The meaning of a user-defined entity instance, and the number, data types and meanings of its attributes, is a matter of agreement between the partners using the exchange structure.
EXAMPLE
DATA; . . . #1=PT(1.0,2.0,3.0); ---------------------> CONVENTIONAL ENTITY INSTANCE #2=PT(1.0,2.0,5.0); . . . #12=!MYCURVE(0.0,0.0,0.0,1.0,$,$,$); ----> USER DEFINED ENTITY INSTANCE . . . ENDSEC;
NOTE Rather than use the user-defined syntax defined in this clause, it is recommended that an implementation define an EXPRESS schema for the user-defined information and encode this information in a separate data section.
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