JADE external database coexistence provides:
Mapping technology to enrich relational schemas with object model semantics
Tables (base, derived, or predefined views) mapped to subclasses of
Columns mapped to attributes
Foreign key definitions are used to determine inverse relationships
Tuples (or rows) map to instances of external classes
Each external database is represented by a subclass of
Object identifier to primary key mapping enables JADE to uniquely identify a tuple and map this to a proxy object in JADE
Inverse relationships can be defined and implemented using references to class types
Multiple-valued properties can be implemented with
JADE can coexist with existing legacy or heritage relational databases in a seamless fashion. JADE provides the External Schema Wizard, to enable you to map your relational database to a JADE object model. (For details about using the External Schema Wizard, see Chapter 3, "Transforming an External Relational Database".)
You can map one or more external relational databases into a JADE object model, by using a Global Conceptual Schema (GCS). The GCS provides a high-level integrated view of external relational databases as part of an existing JADE schema, hiding structural differences between the JADE object model and the relational model, giving the appearance of accessing a single unified database. The relationships between tables in the relational database are mapped to bi-directional relationships using inverse references.
Access relational objects in an external database in a procedural manner, by using the JADE language rather than constructing Structured Query Language (SQL) statements. The External Schema Wizard enables you to map:
Tuples (which may be the result of a project/join or a view) to objects
SQL types to JADE primitive types
Joins to bi-directional relationships based on foreign and primary keys
The mapping is specified declaratively rather than programmatically, to reduce coding requirements and to increase flexibility.
The schema mapping technology is supported by Open Database Connectivity (ODBC), which provides the gateway to access relational databases. ODBC is used during the schema transformation phase to access catalog information, and at run time to populate virtual object instances using SQL queries. As ODBC uses SQL as its database access language, a single application can access different database management systems with the same source code. The JADE query engine calls functions in the ODBC interface, which are implemented in drivers; that is, database-specific modules.