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GCHQDeveloper42 edited this page Mar 25, 2024 · 3 revisions

HQDM Framework

Version 1.0

This part provides the full data model that I have been working through in this book as an EXPRESS schema including both the EXPRESS-G diagrams and the lexical EXPRESS that is computer interpretable, descriptions of the diagrams, and definitions of the entity types and relationship types on each diagram. It is intended as a reference document and an extension to the data model fragments that I introduced in Part 3. This schema was developed using Jotne EPM Technology's EDMVisualExpress data modelling tool. This part covers one way in which a data model may be published by VisualEXPRESS. It may also be published as a website. I intend to publish this schema as a web resource. You should be able to find it by searching the web for the schema name. The data model presented here is broadly compatible with ISO 15926-2, but there are four key differences.

  1. The first is that the metamodel for relationship takes a different approach. The approach in ISO 15926-2 is a little cumbersome, in particular in the way that n-ary relationships are represented. This has little significance since the implementation environment will determine the way that 199 the metamodel will be implemented; what is presented here is a statement of requirements.
  2. The second area of difference is in the way that representation is modelled. In ISO 15926-2, the involvement of those who interpret the sign or pattern was optional. This is clearly a weakness, and I have remedied this.
  3. The third area is in the classes that are represented as entity types. ISO 15926's possible_individual is equivalent to spatio_temporal_extent in the model presented here, and whole_life_individual is equivalent to individual here. If X is a subtype of possible_individual, then X is equivalent to state_of_X in this model, and class_of_X is equivalent to class_of_state_of_X. ISO 15926-2 does not make explicit the subtypes of whole_life_individual as I have done here. Although this made the ISO 15926-2 data model smaller, I think it also made it a lot less easy to see how it should be used.
  4. The fourth area of difference is in the use of association in this data model. An association is a state that consists_of its participants. In ISO 15926-2, these are modelled as relationships between the states, rather than as an association that consists_of the states. A mapping of the key entity types in the schema presented here to ISO 15926-2 is presented in Appendix A.

Entities

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