This allows a model to be divided into submodels, with obvious bene?¬?ts
for manageability and multiuser use. It also provides essential capabilities for reusing
parts of models, for example, building product variants from a subset of all graphs.
Larger-scale concepts can also be added above the graph. Just as a related set of
graphs forms a model, a related set of models can be collected into a project, and
projects themselves can be collected into repositories. The exact details are not
important, but something extra is often needed in addition to the basic concept of
graph.
Objects as Property Values In a version 1.0 DSM environment, objects in
models can often only have properties whose values are simple strings, numbers, or
Booleans. Surprisingly, even the humble string can cover almost all the data storage
needs of most modeling languages. Even numbers are relatively rare: they tend to be
needed more in the metamodel constraints or in systems generated from models. In
models, most ?¬?elds that would commonly hold a number tend to bene?¬?t from being
strings, as this allows the substitution of a variable or named constant rather than a
literal number.
The most common type of property value after strings is a reference to another
object. This provides a powerful way to integrate models: by referring directly to
another object, rather than just typing its name, a modeler solves a major maintenance
headache.
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