IEC 62016-2003 pdf – Core model of the electronics domain

IEC 62016-2003 pdf – Core model of the electronics domain.
2 Reference documents IEC 61690-1:2000, Electronic design interchange format (EDIF) – Part 1: Version 300 IEC 61690-2:2000, Electronic design interchange format (EDIF) – Part 2: Version 400 ISO 13030-11:1994, Industrial automation systems and integration – Product representation and exchange – Part 11: Description methods: The EXPRESS-I language reference manual 3 General modelling issues This standard describes the general modelling techniques and conventions used by the Core Model. The most important concept discussed here is that of relationship between entities (ownership and reference). In addition, issues such as uniqueness in aggregates, default values, empty sets and model topology are presented. 3.1 Ownership and reference An object is said to be the “owner” of another object, if the latter can only exist in the context of the former. From the point of view of the information model, this means that an instance of the “owned” object can exist if, and only if, there is an instance of the owner object. Any given instance of an object must have exactly one owner. Some examples of owner relationships are provided below. By contrast, if an object references another object, the existence of the latter is not dependent on the existence of the former. In the information model this means that the existence of an instance of the referenced object is not related to the existence of any instance of the object that references it. A given instance may be referenced by any number of other instances unless stated otherwise by a constraint. Generally speaking, the referencing mechanism provides a way of sharing data whereas the ownership dependence is used to create a scope for the objects and to control their existence. The difference between the two types of relationship is important because of their effects in an actual implementation.
In this example, ownership is modelled straightforwardly by using the EXPRESS INVERSE clause. Its meaning is that, for every instance of a cell, there is exactly one instance of the library that contains that cell instance. There are cases, however, when an object may have several potential owners. The example in Figure 2 shows that a documentation object may be created in the context of a connectivity_generic_net or a connectivity_generic_bus, etc. The owner relationship is modelled by using the INVERSE clause. Its meaning is that there may exist, at most, one instance of the connectivity_generic_net and, at most, one instance of a connectivity_generic_bus, etc, that contain a given documentation instance. However, any instance of the documentation may exist as a member of the “document” SET in a connectivity_generic_net or as a member of the “document” SET in a connectivity_generic_bus, etc, but not as all of them. Therefore, a domain rule (the WHERE clause) is used in order to ensure that there is only one owner of the documentation instance in the database. Of course, there are other objects that reference that documentation instance.
4 Concepts This chapter describes the fundamental concepts defined by the Core Model. These concepts may be thought of as creating a hierarchy which is abstract at its higher level and becomes progressively more detailed. At the highest level of the structure, an information_base may contain designs and libraries. Each library is a collection of cells which are grouped according to a set of common characteristics. A cell is the main design object which may be instantiated later in another cell, thus creating a design hierarchy. A cell may be connected to other cells by means of its interface. These concepts are described in the following sections. 4.1 The information base An information_base describes the data that can be found in the database of a compliant CAD system. This information may include libraries, designs, global_ports and global_port_bundles and unit definitions. The Core Model is an information model that describes one information base. All the entities defined in the Core Model belong, directly or indirectly, to the information_base object. The model of the information_base entity can be found in the information_base_model schema. A partial EXPRESS-G diagram is also available. 4.2 Global ports and global port bundles Certain ports such as GND, VCC or clocks are used in common by several modules of an electronic circuit. The Core Model describes this by using the concept of global port, which is modelled by the global_port entity. The global_ports are defined in the information_base and are, therefore, visible in all the cells and designs defined in this information base.