11.3. Relational Model Sequencer UUIDs

As mentioned above, the Red Hat JBoss Data Virtualization model sequencer can operate in two modes. The behavior you choose will dramatically change what you can do with the sequenced relational models.

The first mode reuses the "xmi:uuid" identifiers on each object in the model as the "jcr:uuid" node identifiers. In this mode, the sequencer represents each model reference as a JCR WEAKREFERENCE, making it very easy to navigate and query relationships. However, there is one major disadvantage of this approach: each time a model is uploaded into the repository, the sequencer will override any output generated by earlier sequencing operations upon that file (or other versions of it). Thus, the sequenced representation of an uploaded model can ever appear only once within the repository, even though different versions of that model might exist in the repository at different locations. This may be desirable in some situations, but for most situations it is not acceptable.

In the second mode of operation (which is the default mode), there is no correlation between the model's "xmi:uuid" and "jcr:uuid" node identifiers. Various versions of a given model can be uploaded into the repository at multiple locations, yet each model's relational schema will exist in the repository. The downside of this approach is that references are no longer simply WEAKREFERENCE properties. Instead, each single-valued reference will be represented as a series of four properties: where "{referenceName}" is the name of the model reference. Multi-value references are also represented as a series of four properties, but with a slightly different naming pattern: Here, "{singularReferenceName}" is the singular form of the model reference name, and "{pluralReferenceName}" is the plural form of the model reference name. For example, for a reference named "columns", the "{singularReferenceName}" value would be "column" and the plural form is "columns". If the reference name is "properties", the singular form is "property" and the plural form is "properties". (ModeShape uses a novel algorithm to determine the singular and plural forms of many English words.)

References to model objects within the same model are easily resolved upon sequencing, and so we set all of the properties (regardless of the mode). However, references to objects in other models cannot be resolved at sequencing time.