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EPOS architecture

The basic structure of a PSEE has a DBMS at its core and all of the tools of the environment form a layer around it.
EPOS extendes such a model by having three layers around its database.
The EPOSDB [Mun93] is a client-server DBMS. It provides the system with uniform versioning (according to the change oriented paradigm, RIFERIMENTO) and an object-oriented data model.
All the accesses to the database are performed within long, nested and cooperating transactions gif. Every transaction is connected to a corresponding file-based workspace. The data are extracted from the database ( check-out) at the beginning of the transaction. When it commits (i.e. when it ends regularly), the modified data are put back again ( check-in).

Here are the three layers surrounding the EPOSDB:

  1. A reflexive and fully object-oriented PML, called SPELL that unifies and extends the Data Definition Language (DDL) and Data Manipulation Language (DML) of the underlying database.
    SPELL employs the Object-Oriented [Rum87] paradigm. This layer supports the Analysis/Design meta-activity (PM2).

      
    Figure 1.1: The layered architecture of EPOS

  2. A Tasking Framework for the definition and concurrent execution of task networks, with associated tools and humans (meta-activity PM4). The execution is performed the Execution Manager (one per transaction) which invokes external tools through a Broadcast Message Server (BMS).
  3. Application or domain-specific process models. They include both Process Schemas. Application specific types gives the meta-tool (mainly Execution Manager and Planner) the domain knowledge for enacting the process model.
    All activities and products are described through SPELL.


Passani Luca
Mon Feb 20 21:59:27 MET 1995