Attribute represents unique property of an Element. In OOP: property of a class.

An Element may have 1..n attribute instances. Attribute instances of an Element are accesible via it's Attributes collection. AutoCAD treats attributes as both XData records and OpmX properties. Databases treat attributes as table columns (where attribute Name represents column name).

Collection of Attributes accessible by attribute Name.

Connection is commonly used for Constraints that narrow actual instance of attribute value to a set of values found within external catalog (database).

If catalog contents changes after instantiation of an object model, the model needs to get reinstantiated - this is due to the fact that classes utilizing external connections are actually copying contents of the catalog into the memory-resident data set for the reasons of faster data access.

Collection of Connections accessible by connection Name.

Purpose of constraint is to narrow (to constrain) actual values that get written into the per-entity instantiated Attribute. For example, you might want to contrain named Attribute values to predefined set of numbers or strings, expression-based ranges, or utilize already instantiated Connection to fetch the predefined data set within external catalog (database).

Collection of Constraints accessible by constraint Name.

Domain represents a logical set of instantiated Elements found within object model. You can not reference an Element not instantiated within model's Elements collection. Domains may form hierarchical structures (binary trees), each of them referencing 0..n existing Elements. Each domain may also reference it's parent domain, thus promoting it to a superset of referenced elements via inheritance.

Logical sets of elements may get utilized by application for various purposes, i.e. to form specific topologies, denote hierarchy of referenced elements, etc.

Collection of Domains accessible by domain Name.

Extension class providing global domain object model (DOM) capabilities.

Element is a basic building block of an object model. You may refer to it as to an OOP class (type). Each entity class, either graphical or non-graphical, relates to instantiated element found within Elements collection.

Collection of Elements accessible by element Name.

Base class for object model schema features (i.e. Domains, Elements or Attributes). Implements IEquitable interface in a manner that two features are equal if their Names match (please note - this comparision is case sensitive).

Lookup represents a catalog (database) query definition commonly used by Constraint object.

When object model gets initialized within application that utilizes it - all defined lookup queries get executed and their results stored in memory-resident datasets (see Dictionary) for faster data access. If catalog contents changes after instantiation of an object model, lookup queries' results need to get refreshed.

For the sake of speed lookup implements neither type nor validity checking on underlying Connection objects.

Inclusive value range definition used by Constraint.

Valid range is being defined via MinExpression and MaxExpression logical expression strings evaluated during run-time. For more info on conditional expressions and methods of their validation see Expression.

Represents the version number for actual Model instance. Keep in mind that two Model instances are comparable by Version only if their Names match.