POSC Specifications
Version 2.3
Relational Implementation Methodology


Epicentre Sample Relational Implementation

Because Epicentre is a logical data model, it is not directly implementable as a physical database. Epicentre is documented precisely in the EXPRESS1 language but EXPRESS is not the equivalent of a data definition language (DDL), like Structured Query Language (SQL) DDL. To build a POSC data store, it is necessary to transform Epicentre EXPRESS into a set of DDL statements using rules consistent with the target data store's database management system (DBMS). POSC refers to this process as projection.

Creating a physical implementation of the Epicentre Logical Data Model can be divided into three main steps (see Figure Epicentre Framework):

Epicentre Framework

  1. Subset the logical model as necessary based on the scope of data the target implementation is intended to hold. See the POSC Subsetting and Extension specification for a discussion of this subject.
  2. Project the subsetted logical model to a physical schema. In the case of a relational implementation, this consists of creating a DDL file of CREATE TABLE statements that define the valid tables and columns that represent the logical subset.
  3. Apply the referential data integrity enforcement mechanism for the data store. This can be accomplished by applying integrity constraints and triggers in the relational database management system (RDBMS), applying integrity constraints through the DAE compatibility layer and/or documenting procedures to be followed by the people and applications that maintain the data.

POSC and others have projected versions of Epicentre into several different types of database DDL. POSC has built a Relational Projection Tool that can be used to create four sets of SQL DDL: Oracle7, ANSI SQL92, Informix and Sybase.

A strict requirement for any projection of Epicentre is that it should maintain a linkage from Epicentre's logical entities to their physical representations in the database. This is necessary in order to implement the POSC Data Access and Exchange application programming interface and to have an unambiguous understanding of the data in a data store for the purpose of data exchange. POSC supports these requirements in its Compatibility Layer Sample Implementation by the definition of a set of structure tables which map Epicentre entities to their equivalent representations as relational tables. See the POSC Projection Meta Model specification for a description of these structure tables.

POSC refers to its projected relational DDL plus the populated structure tables as an Epicentre Sample Relational Implementation. The purpose of this document is to show the methods and rules that will be used to create a POSC Epicentre Sample Relational Implementation.

New in Version 2.3


This Relational Implementation Methodology is intended to specify how POSC will project a version of Epicentre in order to create an Epicentre Sample Relational Implementation. An Epicentre Sample Relational Implementation is intended to serve as a sample implementation of the Epicentre Logical Data Model from which it is projected. Other POSC-compliant relational implementations of Epicentre may be created so long as they support the POSC Data Access and Exchange application programming interface. This requires that the projection method maintain a linkage between the Epicentre logical entities and their physical representations. Because of the impossibility of attaining a single relational implementation of Epicentre that is optimally tuned for performance and storage for every environment, the reader should be aware that a generic relational implementation may or may not be suitable for the specific applications they require.


This document is intended for the following audience:


POSC has developed the Relational Implementation Methodology through an open process of information exchange with the petroleum industry, its related service industries, and various regulatory bodies. The open process has provided a forum for POSC members to contribute ideas, requirements, and recommended solutions to meet the requirements. We would like especially to thank the following for their contribution.

1EXPRESS Language Reference Manual, ISO International Standard 10303-11, Product Data Representation and Exchange - Part 11, TC184/SC4/WG5, March 1994.

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