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Databases and Systems

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250<br />

CORBA Wrappers<br />

Figure 2: Relationship of Conceptual Model, DB Schema <strong>and</strong> IDL<br />

Generally, today’s databases do not provide CORBA interfaces to their data. It is<br />

therefore necessary to build a so-called wrapper – a program which implements IDL<br />

interfaces for already existing “legacy systems”. This section will discuss some of the<br />

technical issues involved for a fine-grained CORBA interface.<br />

Figure 3: CORBA wrappers make existing DBs available through the ORB<br />

Registering Large Numbers of Objects<br />

<strong>Databases</strong> can contain millions of entries. The ORB has to be able to keep track of<br />

the connection between these database entries <strong>and</strong> the corresponding CORBA object<br />

references. The general idea is to encode a unique identifier of the database entry in<br />

the object reference. It is therefore essential that such an object identifier or key<br />

attribute exists in the database. Most ORBs have their own proprietary way of<br />

implicitly registering large numbers of objects. The recently adopted Portable Object<br />

Adapter (POA) st<strong>and</strong>ardizes this possibility.

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