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Difference between revisions of "Higgins/ModelAPIs"

Line 19: Line 19:
 
* getAttributes() returns: typical attributes about this person (things like a homeAddress and phoneNumber)
 
* getAttributes() returns: typical attributes about this person (things like a homeAddress and phoneNumber)
 
* getType() returns: an identifier for this person's model entity.  assume it's called “http://example.com/some/name/space#Person”
 
* getType() returns: an identifier for this person's model entity.  assume it's called “http://example.com/some/name/space#Person”
 +
** Note that getType is only a convenience for getTypeEntity().getEntityID()
 
* getTypeEntity() returns: some impl of IEntity, assume it returns a PersonModel.class
 
* getTypeEntity() returns: some impl of IEntity, assume it returns a PersonModel.class
  

Revision as of 11:10, 19 June 2008

{{#eclipseproject:technology.higgins}}

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Problem

Today, IdAS defines a set of special interfaces for accessing a context's model elements. There are a number of problems with these interfaces:

  1. They are 'fixed' in nature. The only way to represent extra information about the model of context elements is to revise these interfaces. For example, say there's a need to associate an image with the attribute called “http://example.com/some/name/space#telephoneNumber” (this image might be used by a management UI). To make that association we need a new method like IAttributeModel.getManagementImage().
    1. Even if we felt like it's ok to revise the current I*Model interfaces, we do not know what kinds of information will need to be associated with the models of elements in a context. It may be the case that some people will have needs that we think are unworthy of revising the interfaces for. For example, say someone wants to associate an astrological symbol to each different attribute model. Does that mean we should add a new IAttributeModel.getAstrologicalSymbol()?
  2. There is no way to update a context's model. We have a need to be able to add models for new entity types, attribute types and so-on. We also need to be able to change existing models (such as changing the cardinality of an attribute). Also, we may need to remove models.
  3. We cannot look up a model with partial information. For example, say I know there's an attribute with the word "telephoneNumber" in its ID, but I don't know the entire ID. It would be nice to be able to have a way to find what I need without enumerating through the entire set of attribute models.

Proposal

It may be better to move away from the existing special interfaces for the purpose of defining the model of elements, but instead simply re-use the existing interfaces that are used to access normal information within a Context (entities and their attributes).

Following is a proposal which shows how these model entities might look. To illustrate the proposal, we start by showing how an instance of a person looks (nothing new) and then examining the model entities that govern instances of entities and attributes:

A person

Example of an instance of a person entity.

  • Java type: some impl of IEntity. The context provider implements this class
  • getEntityID() returns: the contextually unique ID for this person
  • getAttributes() returns: typical attributes about this person (things like a homeAddress and phoneNumber)
  • getType() returns: an identifier for this person's model entity. assume it's called “http://example.com/some/name/space#Person”
    • Note that getType is only a convenience for getTypeEntity().getEntityID()
  • getTypeEntity() returns: some impl of IEntity, assume it returns a PersonModel.class

A person's model

Now, say we look at the “person model” entity we saw above (we got this either by calling IEntity.getTypeEntity(), or IEntity.getType() followed by IContext.getEntity(EntityID)), we see (NOTE: this entity is a model element):

The "top" entity model

Ok, now let's look at the instance of the entity called “http://www.eclipse.org/higgins/ontologies/2006/higgins#Entity”. This is simply the top-level model definition for all entity model hierarchies. Thus it contains model definitions for things common to all entities:

The model for entity models

What defines an entity model entity? This does:

The model for model elements

Finally, here's the model for model elements:

Note the recursive nature of getType and getTypeEntity above. We could instead return null or throw some well-known exception.

An attribute model

Now for fun, let's look at an attribute's model, and follow that. We'll take the example of “http://example.com/some/name/space#homeAddress”:

The model for attribute models

And here's that the entity identified by “http://www.eclipse.org/higgins/ontologies/2006/higgins#AttributeModel” looks like:

Then of course we have value models. Again from the bottom-up, here's an entity that describes a value type called <TODO: finish this>

<TODO need to be able to specify min/max cardinality on each attributeType associated with a specific entity model so we can preserve the ability to say "person entities must have at least one surname attribute value, and may have a telephone number" without causing all instances of surname to be min=1

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