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1.1 MetaEdit+ data model: GOPPRR

The basic requirement for implementing a modeling language with a metaCASE tool is the specification of the language definition. For this purpose, MetaEdit+ uses the GOPPRR metamodeling framework. GOPPRR specifications of the modeling language are made with the metamodeling tools of MetaEdit+ Workbench. The metamodels thus made are read by MetaEdit+ to configure itself to provide the support environment for the modeling language.

Although more familiar languages from other domains can also capture some of the information necessary in metamodels, GOPPRR is preferred here because it was specifically designed for describing modeling languages. Using a domain-specific modeling language for the task of metamodeling brings the same benefits as the use of DSM in any domain: simplicity, precision, and automation. Languages like UML, MOF and ER were intended for other domains, entailing greater effort, loss of precision, and risk of misunderstanding for the reader.

Before looking at metamodels, we will start with an example model of a simple order handling system (Figure 1–1).

Figure 1–1. A Data Flow Diagram of an order handling system (partial).

This diagram describes the flow of data when handling orders and invoices. On the right of the figure we have labeled some examples of the basic constructs that can be found in all models, whatever their language.
A graph is one individual model, often shown as a diagram
Objects are the main elements of graphs, often shown as boxes or circles
A relationship connects objects together, often shown as a label over the connection
A role connects an object into a relationship, shown as a line and often an arrow-head
A property is an attribute characterizing one of the above, often shown as a label
We will call these basic constructs metatypes. The table below lists some example instance elements of this model, their types, and their metatypes.
Order handling
Data Flow Diagram
Process invoice payments, Customer
Process, External
Payment history, Verified orders
Data Flow
Arrow-head at Accounts receivable
From, To
"Process invoice payments", "3"
Process Name, Process Number
In addition to these metatypes, some modeling languages also use ports: specific points on the edge of an object symbol to which roles can connect. Together, these six metatypes form the concepts of GOPPRR, which we will describe in more detail below.

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