The Object Protocol Model Data Management Tools

The OPM data management tools provide facilities for developing and accessing databases defined using OPM, for constructing OPM views of existing relational databases and structured files, for representing database schemas using alternative data-models, for publishing schemas in various formats, and for querying databases through uniform OPM views. The OPM multidatabase tools provide facilities for exploring multiple heterogeneous databases that have either native OPM schemas or retrofitted OPM views. We will briefly describe each of the OPM data management tools below.

The OPM Database Development Tools

OPM schemas can be specified using either a regular text editor or using the graphical OPM Schema Editor. The OPM Schema Editor is implemented in Java and provides a graphical interface implemented using the Java Abstract Windowing Toolkit (AWT). The tool allows object and protocol structures to be specified incrementally by defining new OPM classes, modifying existing OPM classes and defining attributes of classes. OPM schemas can be also examined graphically on the Web using the OPM Schema Browser. The OPM Schema Editor and the OPM Schema Browser provide facilities for generating Postscript diagram, LaTeX document and HTML file representations of OPM schemas.

OPM schemas are maintained as ASCII files that can be passed to the OPM Schema Translators described below, in order to generate the corresponding DBMS-specific database definition and constraints.

Individual OPM schemas or several related schemas can be documented in a Database Directory and Schema Library (DD&SL). A DD&SL contains information on individual databases, such as database names, underlying DBMS, access information, and the database schemas represented in OPM and other alternative notations, such as the Extended Entity-Relationship (EER) model, the relational model, and the ASN.l data exchange notation. In addition the DD&SL contains information about the relationships between databases represented in the DD&SL, or inter-database links, which can be used in exploring across databases and formulating multi-database queries. The DD&SL is used by the Multidatabase Query Tools described later, in order to provide the information necessary formulating multidatabase queries. The information in a DD&SL may also be automatically converted to a hierarchy of HTML pages, so that the DD&SL may also be browsed using a Web browser, such as Netscape or Explorer (see [6] for details).

The OPM Schema Translator translates OPM schemas into relational database definitions and database procedures implementing the OPM retrieval and update methods [2]. Informally, the translation of an OPM schema into a relational database definition entails mapping every OPM object or protocol class C into a primary relation R. Depending on their type (primitive, abstract, simple, tuple, etc.), non-derived attributes of C are mapped into local attributes ofR, foreign-key attributes of R, or additional auxiliary relations with appropriate foreign-key to primary-key references. Derived OPM attributes are mapped into relational procedures that are used for computing their values at run time. The OPM Schema Translator also generates a mapping dictionary containing information on the OPM to relational database mapping.

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