EEX Specification

Version: 0.5 2017.09.15 AET

"EEX" is acronym for EDM EXPRESS Extension Schema, and is also the file extension used for such files.

EXPRESS_EXTENSION_SCHEMA Declaration

EXPRESS_EXTENSION_SCHEMA   extensionSchemaName FOR expressSchemaName; <body>  END_EXPRESS_EXTENSION_SCHEMA;

EXPRESS_EXTENSION_SCHEMA   extensionSchemaName {‘GUID’} FOR expressSchemaName;<body>  END_EXPRESS_EXTENSION_SCHEMA;

The reason for the optional GUID is to be able to track/label one particular version of an extension schema and population(data).

Example: exporting a population including “extension schema data” on a step file package. When importing such step file package, the GUID is used to ensure that the extension schemata in the importing DB is exactly the same as in the exporting DB. There will be an option in write/read step file package to include exporting/defining of the extension schemata.

ENTITY Declaration

ENTITY declarations in an extension schema have the same syntax as in an Express schema except the following:

Declarations not supported: UNIQUE , WHERE
Extension: GENERIC_ENTITY is allowed as domain for all attribute types.
Extension: INVERSE attribute may be declared: ALL_LOCAL_REFS_TO_ME : SET OF GENERIC_ENTITY; -- no “ FOR ‘attributeName’ “
- The attribute will return a set containing all instances that refers this instance within the same model
Extension: INVERSE attribute may be declared: ALL_CROSS_MODEL_REFS_TO_ME : SET OF GENERIC_ENTITY; -- no “ FOR ‘attributeName’ “
- The attribute will return a set containing all instances that refers this instance within the same database - all models

Example

-- extend the IFC schema with a window suitable for cars	
ENTITY xifcWindShield SUBTYPE of IfcWindow;		
	fitsMakes : LIST OF xifcVehicle; -- list of car makes that this window will fit in
END_ENTITY;
 
ENTITY xifcVehicle;		
	brand : STRING; 	-- i.e. 'Ford'		
	model : STRING;  	-- i-e 'T'        
	year  : STRING; 	-- i.e '1921-1924'    
END_ENTITY;

ENTITY_EXTENSION Declaration

The ENTITY_EXTENSION – END_ENTITY_EXTENSION as earlier agreed, plus the same extensions for attribute declarations as for ENTITY.

ENTITY_EXTENSION ‘entity_extension_name’ FOR ‘expressEntityName’; <body>  END_ENTITY_EXTENSION;

ENTITY_EXTENSION ‘entity_extension_name’ FOR SUBTYPES ‘expressEntityName’; <body>  END_ENTITY_EXTENSION;

Additional rules:

EESR #22: A name of an ENTITY_ EXTENSION declaration must only be unique in the collection of all ENTITY_EXTENSION declarations in the actual extension schema. (22)
- Technically there is no problem to allow an ENTITY_EXTENSION name to have the same name as other declarations (ENTITY, TYPE, FUNCTION …etc), but for “readability” we may not permit it.

EESR #23: There must be only one ENTITY_ EXTENSION declaration for the same entity in one extension schema
- With the use of SUBTYPES declaration, there may be implicitly more than one ENTITY_ EXTENSION that extends the same entity:
- Example
  Example:
```
     ENTITY_EXTENSION Extend_ifcWindow  FOR ifcWindow;
```
```
          ……
```
```
     END_ ENTITY_EXTENSION;
```
```
 
```
```
     ENTITY_EXTENSION Extend_ifcRoot FOR SUBTYPES ifcRoot;
```
```
              ……
```
```
     END_ ENTITY_EXTENSION; 
```
  In this example, both the Extend_ifcWindow (explicitly) and Extend_ifcRoot (implicitly) will extend the ifcWindow entity.

We can discuss how many of the ”extension schema rules checking” we implement in the compiler and how many we implement in the edmCloseExtensionSchemaCompilerModel() (similar as edmCloseCompilerModel()).

Supported EXPRESS Declarations

The following Express declarations are supported:

TYPE - without the WHERE
ENTITY – with the above listed restrictions and extensions
Subtype_constraint – to be decided???
CONSTANT
FUNCTION
PROCEDURE

Not supported EXPRESS Declarations

The following Express declarations are not supported:

SCHEMA
RULE (Rules can be written in separate RULE_SCHEMA)

New tokens (reserved words):

         ALL_CROSS_MODEL_REFS_TO_ME
         ALL_LOCAL_REFS_TO_ME
         END_ENTITY_EXTENSION
         ENTITY_EXTENSION
         END_EXPRESS_EXTENSION_SCHEMA
         EXPRESS_EXTENSION_SCHEMA

Compiler checking

In addition to the “standard compilation time checking” during defining (compilation) of an extension schema, the following will be checked:

EESR #31: NumberOfExtensionSchema for ExpressSchema < MAX_EXTENSION_SCHEMATA for an Express schema
EESR #32: ExtensionSchema name already exist for the particular Express schema
EESR #33: All ENTITY names must be unique in the collection of Express schema and all extension schemata for the actual Express schema.
EESR #34: In addition to the rule in the Express language for “unique attribute names in an Entity declaration” , attribute names must be unique in the collection of all ENTITY_EXTENSION for a particular entity in all extension schemata for the actual Express schema.
- The ALL_CROSS_MODEL_REFS_TO_ME and ALL_LOCAL_REFS_TO_ME are exceptions to this constraint. When a combination of extension schemata results in more duplicates of these attributes, this “problem” will be resolved when the actual model will be created, such that the actual entity instances will have only one occurrence of each of these attributes;

We can discuss how many of the ”extension schema rules checking” we implement in the compiler and how many we implement in the edmCloseExtensionSchemaCompilerModel() (similar as edmCloseCompilerModel()).

Syntax Illustration 0.5

(**
	Check basic elements for EXTENSION_SCHEMA
	Should compile with no errors	
*)
EXPRESS_EXTENSION_SCHEMA  EEX_1011 FOR IFC4;
GLOBAL
	gGeneric		: GENERIC;
	gGenericEntity	: GENERIC_ENTITY;
	geexEntity		: eexEntity;	
END_GLOBAL;

CONSTANT
	cInteger : INTEGER := 1;	
END_CONSTANT;

    ENTITY eexEntity;
        explicitAttr1 : INTEGER;
        explicitAttr2 : GENERIC_ENTITY;
	DERIVE
		derivedAttr1  : STRING := foo1(SELF);
		derivedAttr2  : STRING := foo2(SELF);		
    INVERSE
		cross_references : SET OF GENERIC_ENTITY FOR ALL_CROSS_MODEL_REFERENCES_TO_ME;
		local_refs: SET OF  GENERIC_ENTITY FOR ALL_LOCAL_REFS_TO_ME;		
    END_ENTITY;
 

    ENTITY eexTask SUBTYPE OF(ifcTask);
        explicitAttr1 : INTEGER;
    END_ENTITY;
 
    ENTITY_EXTENSION extToIfcSpace FOR  IfcSpace;
       (* Attribute name must be unique within the extended entity (ifcxx1), may be same as
          attribute names in super type Entity. When so, this extended attribute must be
          accessed by name using "full qualified attribute name".
          The attribute domains can be any domain in the actual schema or domain (instance type)
          defined in the current extension schema
       *)
       extendedExplicitAttr1 : STRING;           -- any simple data type can be used, not defined types
       extendedExplicitAttr2 : GENERIC_ENTITY;   --sdaiINSTANCE of any type. can be used as link to instance in any other model.
       extendedExplicitAttr3 : SET OF GENERIC_ENTITY;
    DERIVE
        extendedDeriveAttr : SET OF GENERIC_ENTITY := foo4(SELF);
    INVERSE
		cross_references 	: SET OF GENERIC_ENTITY FOR ALL_CROSS_MODEL_REFERENCES_TO_ME;
		local_refs			: SET OF GENERIC_ENTITY FOR ALL_LOCAL_REFS_TO_ME;		
		-- extendedInverseAttr 	: SET OF GENERIC_ENTITY FOR (entityx.explicitAttr1, entityx.explicitAttr2, ...entityz.explicitAttr5);
    END_ENTITY_EXTENSION;
	

    ENTITY_EXTENSION extToIfcElementSubtypes FOR SUBTYPE IfcElement;
       (* same as ENTITY_EXTENSION except that all extensions will be valid for all subtypes of the extended entity, i.e., all subtypes of IfcElement  *)
       extendedExplicitAttr1 : STRING;           -- any simple data type can be used, not defined types
--    INVERSE
--		extendedInverseAttr : SET OF GENERIC_ENTITY FOR (entityx.explicitAttr1, entityx.explicitAttr2, ...entityz.explicitAttr5);
    END_ENTITY_EXTENSION;
	
	FUNCTION foo1(arg : GENERIC) : STRING;
		RETURN('typename');
	END_FUNCTION;
	
	FUNCTION foo2(arg : GENERIC_ENTITY) : STRING;
		RETURN('typename');
	END_FUNCTION;


	FUNCTION foo4(arg : GENERIC_ENTITY) : SET OF GENERIC_ENTITY;
	LOCAL
		result : SET OF GENERIC_ENTITY := [];
	END_LOCAL;
		RETURN(?);
	END_FUNCTION;

	
	PROCEDURE poo1(arg1 : GENERIC;VAR arg2: GENERIC);
		arg1.explicitAttr1 := 2;
		arg2.explicitAttr1 := 2;
	END_PROCEDURE;

	PROCEDURE poo2(arg1 : GENERIC_ENTITY;VAR arg2: GENERIC_ENTITY);
		arg1.explicitAttr1 := 2;
		arg2.explicitAttr1 := 2;
	END_PROCEDURE;



END_EXPRESS_EXTENSION_SCHEMA;

Historical:

History

ExtensionSchema 0.1

EXPRESS_EXTENSION_SCHEMA   ExtensionSchemaName FOR IFC2X3;

    EXTEND_ENTITY   ifcxx1;
       (* Attribute name must be unique within the extended entity (ifcxx1), may be same as
          attribute names in super type Entity. When so, this extended attribute must be
          accessed by name using "full qualified attribute name".
          The attribute domains can be any domain in the actual schema or domain (instance type)
          defined in the current extension schema
       *)
       extendedExplicitAttr1 : STRING;           -- any simple data type can be used, not defined types
       extendedExplicitAttr2 : GENERIC_ENTITY;   --sdaiINSTANCE of any type. can be used as link to instance in any other model.
       extendedExplicitAttr3 : SET OF GENERIC_ENTITY;
    INVERSE
       ALL_CROSS_MODEL_REFERENCES_TO_ME : SET OF GENERIC_ENTITY;  -- reserved name, keeps all references from other models
       extendedInverseAttr : SET OF GENERIC_ENTITY FOR (entityx.explicitAttr1, entityx.explicitAttr2, ...entityz.explicitAttr5);
    END_EXTEND_ENTITY;

    EXTEND_ENTITY_AND_SUBTYPES   ifcxx2;
       (* same as EXTEND_ENTITY except that all extensions will be valid for all subtypes of the extended entity, i.e., all subtypes of ifcxx2 *)
       extendedExplicitAttr1 : STRING;           -- any simple data type can be used, not defined types
       extendedExplicitAttr2 : GENERIC_ENTITY;   --sdaiINSTANCE of any type. can be used as link to instance in any other model.
       extendedExplicitAttr3 : SET OF GENERIC_ENTITY;
    INVERSE
       ALL_CROSS_MODEL_REFERENCES_TO_ME : SET OF GENERIC_ENTITY;  -- reserved name, keeps all references from other models
       extendedInverseAttr : SET OF GENERIC_ENTITY FOR (entityx.explicitAttr1, entityx.explicitAttr2, ...entityz.explicitAttr5);
    END_EXTEND_ENTITY;
     
    NEW_EXTENSION_ENTITY name;
        explicitAttr1 : INTEGER;
        explicitAttr2 : GENERIC_ENTITY;
        ........
     INVERSE
        .......
        ALL_CROSS_MODEL_REFERENCES_TO_ME : SET OF GENERIC_ENTITY;  -- reserved name, keeps all references from other models
    END_NEW_EXSENSION_ENTITY;

     NEW_NEW_EXTENSION_ENTITY name SUBTYPE OF (entity1, entity2, ... entityN);  -- subtype of any entity or "extended entity" in schema
        explicitAttr1 : INTEGER;
        explicitAttr2 : GENERIC_ENTITY;
        ........
     INVERSE
        .......
        ALL_CROSS_MODEL_REFERENCES_TO_ME : SET OF GENERIC_ENTITY;  -- reserved name, keeps all references from other models
    END_NEW_EXTENSION_ENTITY;

END_EXPRESS_EXTENSION_SCHEMA;

Arnes adjusted proposal out of Hans Karsten initial spec:

Declarations should be like nouns not verbs
Avoid new keywords, there are too many already. Try reusing existing
Use "FOR" to explicit scope to EXPRESS scema
Entity extensions always have own name
Use leading underscore for "EDM extension" ALL_CROSS_.....

ExtensionSchema 0.2

EXTENSION_SCHEMA   ExtensionSchemaName FOR IFC2X3;

    ENTITY_EXTENSION extToifcxx1 FOR ifcxx1 ;
       (* Attribute name must be unique within the extended entity (ifcxx1), may be same as
          attribute names in super type Entity. When so, this extended attribute must be
          accessed by name using "full qualified attribute name".
          The attribute domains can be any domain in the actual schema or domain (instance type)
          defined in the current extension schema
       *)
       extendedExplicitAttr1 : STRING;           -- any simple data type can be used, not defined types
       extendedExplicitAttr2 : GENERIC_ENTITY;   --sdaiINSTANCE of any type. can be used as link to instance in any other model.
       extendedExplicitAttr3 : SET OF GENERIC_ENTITY;
    INVERSE
       _ALL_CROSS_MODEL_REFERENCES_TO_ME : SET OF GENERIC_ENTITY;  -- reserved name, keeps all references from other models
       extendedInverseAttr : SET OF GENERIC_ENTITY FOR (entityx.explicitAttr1, entityx.explicitAttr2, ...entityz.explicitAttr5);
    END_ENTITY_EXTENSION;

    ENTITY_EXTENSION extToifcxx2 FOR SUBTYPE(S) ifcxx2;
       (* supplying SUBTYPES enables all extensions will be valid for all subtypes of the extended entity, i.e., all subtypes of ifcxx2 *)
       extendedExplicitAttr1 : STRING;           -- any simple data type can be used, not defined types
       extendedExplicitAttr2 : GENERIC_ENTITY;   --sdaiINSTANCE of any type. can be used as link to instance in any other model.
       extendedExplicitAttr3 : SET OF GENERIC_ENTITY;
    INVERSE
       _ALL_CROSS_MODEL_REFERENCES_TO_ME : SET OF GENERIC_ENTITY;  -- reserved name, keeps all references from other models
       extendedInverseAttr : SET OF GENERIC_ENTITY FOR (entityx.explicitAttr1, entityx.explicitAttr2, ...entityz.explicitAttr5);
    END_ENTITY_EXTENSION;
     
     ENTITY_EXTENSION name; -- lacking FOR part means a new entity
        explicitAttr1 : INTEGER;
        explicitAttr2 : GENERIC_ENTITY;
        ........
     INVERSE
        .......
        _ALL_CROSS_MODEL_REFERENCES_TO_ME : SET OF GENERIC_ENTITY;  -- reserved name, keeps all references from other models
    END_ENTITY_EXTENSION;


     ENTITY_EXTENSION name SUBTYPE OF (FOR entity1, extendedentity2, ... entityN);  -- subtype of any entity (FOR x) or "extended entity" in schema
        explicitAttr1 : INTEGER;
        explicitAttr2 : GENERIC_ENTITY;
        ........
     INVERSE
        .......
        _ALL_CROSS_MODEL_REFERENCES_TO_ME : SET OF GENERIC_ENTITY;  -- reserved name, keeps all references from other models
    END_ENTITY_EXTENSION;

END_EXTENSION_SCHEMA;

I think this approach also allows for using only "ENTITY" in stead of "ENTITY_EXTENSION", but that is maybe going too far? Or maybe not, ref RULE_SCHEMA.