PDM-UG: External Files
From WikiSTEP
This page belongs to the PDM Usage Guide.
External files in the PDM Schema represent a simple external reference to a named file. The external file may identify a digital file or a physical, 'hardcopy' file. As opposed to a managed 'Document as Product', an external file is not managed by the system - there is no capability for managed revision control or any document representation definitions for an external file.
An external file is simply an external reference that may be associated with other product data. Document/file properties may be associated with an external file as with an identified managed document. In the case where properties differ with different versions, the managed 'Document as Product' approach is recommended.
If a file is under configuration control, it should be represented as a constituent of a document definition view/representation according to 'Document as Product'. In this case, it is actually the managed document that is under direct configuration control; the file is, in this way, indirectly under configuration control. A change to the file results in a change to the managed document (i.e., a new version) - the changed file would be mapped as a constituent of a view/representation definition of the new document version. A simple external reference alone is not configuration controlled, it is just an external file reference to product data.
While managed revision control representing multiple versions and version history is not available for external files, external files may have an optional version identification providing a string labeling the version of the file.
External File Identification
Identification of an external file is done using the entity document_file. The document_file entity is a defined subtype of the entity document. It is also a subtype of the entity characterized_object, which allows association of properties to the identification of an external file.
The Instance Model: EXPRESS entities and attributes
The EXPRESS entities and attributes used to support the requirements of external file identification are illustrated in Diagram 37 below.
Diagram 37: External File Identification Instance Diagram
Document file
The document entity is a subtype of the document entity, and thus works together with the applied_document_¬reference to support the assignment of external files to product data. Document_file is also a subtype of the entity characterized_object, which has local attributes name and description.
Since both super types of this entity define local attributes 'name' and 'description', the subtype document_file has a double inheritance of these attributes. Local constraints defined on the entity document_file specify that the additional attributes inherited from the supertype characterized_object should not be used for valid user data. These constraints specify that the value of the name attribute be an empty string: ' ' and the OPTIONAL description attribute should not be populated.
Attributes
- The id attribute indicates the unique identifier of the external file.
- The name attribute is double inherited. Only the one derived from the document supertype is valid for user data, the nomenclature of the external file. The name attribute inherited from characterized_object should be assigned the empty string.
- The description attribute is double inherited. Only the one derived from the supertype document is valid for user data. The description attribute inherited from characterized_object should be assigned the empty string.
- The kind attribute is a reference to the file "type" classification information.
| ENTITY document_file | Attribute Population | Remarks |
| id | type: identifier = string | |
| SELF\document.name | type: label = string | valid user data for file id |
| SELF\document.description | type: text = string | OPTIONAL |
| kind | type: entity = document_type | |
| SELF\characterized_object.name | type: label = string empty string | not to be used for valid user data |
| SELF\characterized_object.description | type: text = string $ | not to be used for valid user data |
===Preprocessor Recommendations=== Preprocessors must carefully encode the exchange syntax for an instance of document_file to properly handle the multiple inheritance of the attributes name and description. An example instance of document_file is illustrated in Example 33.
The document_file entity requires an associated instance of the entity document_representation_type. The document_file entity constrains the possible values of the attribute document_representation_type.name, as described in Document representation type.
The id attribute is a unique identifier for the external file. Access path information for a file should be represented as a file "source" property.
===Postprocessor Recommendations=== There are no specific postprocessor recommendations.
===Related Entities=== There are no specific related entities.
Document representation type
The document_representation_type entity provides the capability to identify the type of the representation of a particular external file, either digital or physical.
Attributes
- The name attribute is used to identify the particular representation type (either digital or physical) of the associated external file.
- The represented_document attribute is a reference to the associated external file.
| ENTITY document_representation_type | Attribute Population | Remarks |
| name | type: text = string 'digital' or 'physical' | |
| represented_document | type: entity = document | for file identification, this attribute will reference the subtype document_file |
===Preprocessor Recommendations=== For file_identification, the possible values for the name attribute are 'digital' and 'physical'. A digital file represents an electronic file on a computer system. A physical file is the actual paper hardcopy or other physical realization of a file.
===Postprocessor Recommendations=== A value for the name attribute of 'digital' should be interpreted to mean the associated document_file represents an external reference to an electronic digital file. The value 'physical' should be interpreted to mean the associated document_file represents an external reference to a hardcopy file.
===Related Entities=== There are no specific related entities.
Document type
The document_type entity provides the capability to identify the type of an external file for the general requirement of file type classification.
Attributes
- The product_data_type attribute is used to identify the kind of product data in the associated file.
| ENTITY document_type | Attribute Population | Remarks |
| product_data_type | type: identifier = string |
===Preprocessor Recommendations=== There are no specific preprocessor recommendations.
===Postprocessor Recommendations=== There are no specific postprocessor recommendations.
===Related Entities=== There are no specific related entities.
Applied identification assignment
The applied_identification_assignment entity is a subtype of the entity identification_assignment. It allows the actual assignment of an identification_assignment entity to product data, in this case to a document_file entity representing an external file.
Attributes
- The items attribute is used to reference the associated external file.
| ENTITY applied_identification_assignment | Attribute Population | Remarks |
| assigned_id | type: identifier = string | contains the string identifying the version of the external file. |
| role | type: entity = identification_role | for file version identification, this entity should have name attribute value = 'version' |
| items | type : entity = document_file | reference to the associated external file to which the version identification is assigned. |
===Preprocessor Recommendations=== The use of this entity is optional. When applied to a document_file, it represents simple version identification for the external file. It is not to be used for managed revision control. If managed revision control is the requirement, then the 'Document as Product' approach must be used. The value of the attribute assigned_id contains the version identification. This should not be used for managed version control, but rather for an optional label providing additional information about the version of the document that is identified. The value of the role attribute is an instance of the entity identification_role with its name attribute assigned the string 'version'.
===Postprocessor Recommendations=== Postprocessors should recognize this entity as providing version identification label for the associated external file.
===Related Entities=== There are no specific related entities.
Identification role
The identification_role entity in this use case indicates the role of a version identification for an external file.
Attributes
- The name attribute is used to indicate that the related identification_assignment represents a version identification for the associated external file.
- The description attribute is optional additional text.
| ENTITY identification_role | Attribute Population | Remarks |
| name | type: identifier = string 'version' | Contains the string indicating that the related identification_assignment represents a version identification for an external file. |
| description | type: text = string | OPTIONAL |
===Preprocessor Recommendations=== The attribute name should be assigned a value of 'version' in this usage.
===Postprocessor Recommendations=== The name attribute value 'version' should be interpreted as an indication that the associated applied_identification_assignment represents simple version identification for the file.
===Related Entities=== There are no specific related entities.
The Instance Model: STEP exchange file format (ISO10303 Part 21 syntax)
#510=DOCUMENT_FILE('doc_id',,$,#520,,$);
#520=DOCUMENT_TYPE('unspecified type');
#540=DOCUMENT_REPRESENTATION_TYPE('digital',#510);
Although managed revision control representing multiple versions and version history is not available for external files, they may have an optional version identification that provides a string labeling the version of the external file. If multiple versions are represented, the 'Document as Product' approach is recommended.
The Instance Model: EXPRESS entities and attributes
The EXPRESS entities and attributes essential to support the requirements of external files with optional version identification are illustrated in Diagram 38.
Diagram 38: External File with Version Identification Instance Diagram
The Instance Model: STEP exchange file format (ISO10303 Part 21 syntax)
#500=IDENTIFICATION_ROLE('version',$);
#510=DOCUMENT_FILE('doc id','',$,#520,'',$);
#520=DOCUMENT_TYPE('unspecified type');
#530=APPLIED_IDENTIFICATION_ASSIGNMENT('THE VERSION ID',#500,(#510));
#540=DOCUMENT_REPRESENTATION_TYPE('digital',#510);
