1 A data ?¬‚ow diagram of order handling system (partial)
TABLE A.1 Instances, Types, and Metatypes
Instance Type Metatype
Order handling Data ?¬‚ow diagram Graph
Process invoice payments, customer Process, external Object
Payment history, veri?¬?ed orders Data ?¬‚ow Relationship
Arrow-head at accounts receivable From, To Role
???Process invoice payments???, ???3??? Process name, Process number Property
412 METAMODELING LANGUAGE
We will call these basic constructs metatypes. Table A.1 lists some example
instance elements of this model, their types, and their metatypes.
A language usually has additional constructs that are not immediately visible from
one example model. In our example, a process may contain subprocesses that are
speci?¬?ed in another data ?¬‚ow diagram. A language also has a number of constraints
that ensure model correctness and consistency, such as:
. Processes can be connected with data ?¬‚ows to processes, externals, and stores
. Stores and externals can be connected to processes, but not to stores or externals
. Each data ?¬‚ow connects two objects, with one from role and one to role
. Each process must have a process number, unique over all diagrams
. All processes in a diagram must have different process names
A metamodeling language can describe these constraints along with the modeling
constructs.
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