EPA modelling


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As discussed on the main page, EPA uses up to two models to synthesise architectures:

  • The schema, containing the ontology of component and connection types and the network structure constraints (NSCs);
  • The start point (if appropriate), a model of an existing architecture constructed from components linked by connections.

In particular, the NSCs consist of four types:

  • Component number constraints (CNCs) specify the number of components of a given type that may be present in a design, for instance There must be one input gear.
  • Direct connection constraints (DCCs) specify the component types that may be connected together and the connection types that may do so. In addition, they specify the required cardinality of the connection - the number of components of the second type that may be connected to a component of the rst type, and vice versa. For instance, A gear must mesh with at least one other gear (where Gear is an abstract component type that is the parent of the concrete component types Input gear, Output gear and Idler gear). These are similar to relation cardinality constraints used in UML, Object-Process Modelling and the Object Constraint Language (OCL).
  • Fan-out constraints (FOCs) specify the total number of connections of a certain type that components of a certain type may have, for instance An idler gear must have at least two meshes with connections (to avoid "dangling" idler gears at the end of the gear train). If the connection type is directed, an FOC may be defi ned to apply to incoming connections only, outgoing connections only, or both.
  • Indirect connection constraints (ICCs) specify the number of continuous paths that must exist from every component of one type to every component of another type, made up of connections of speci ed type(s), for instance There must be exactly one path of meshes with connections from the input gear to the output gear (to transmit torque from the input to the output without loops in the gear train). The direction of directed connections may be either considered or ignored when checking for paths. Optionally, the number of components of particular types on the path may also be speci ed.

Graphical models of both may be constructed as CAM workbooks of the "EPAPalettev2" type. The tool icons corresponding to each type of element are as follows:

  • Component:
  • Connection:
  • Component type:
  • Connection:
  • Direct connection constraint:
  • Fan-out constraint:
  • Indirect connection constraint:

Component types have embedded CNCs for simplicity, but there is also a tool to create a separate CNC:

Properties of elements (their name, concreteness/abstractness, and numerical ranges for constraints) may be set by double-clicking on the relevant element and entered into the resulting dialog box. The numerical aspects are expressed by ranges with a minimum and a (potentially infinite) maximum for the quantity concerned - an infinite upper bound is expressed by "*" (without quotes). A key to the syntax used with these elements is shown in the image below (click to enlarge). You may also find it useful to look at some of the example models downloadable from the main page.