1.4 Conventions/Terminology
There are a number of different methodologies for structured Analysis/Design and Data Modeling. Each has its own terminology. Most methodologies use the same underlying constructs, although they call them by different names. LANSA has selected the most useful constructs which are common to most methodologies.
The following list describes how some of the terminology is used in the LANSA Logical Modeler:
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Abstraction |
A container object used to group entities. It is not an entity. It is not used in relationships.
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Attribute |
An element which is associated with (attached to) an entity. For example, the Customer Name is an attribute of the Customer entity.
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Cascade |
If the identifying element (key) of an entity changes, then the keys of any relationships defined from that entity will change. For example, when the key of a Parent entity changes, the keys of any child entities will also change.
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Element |
A basic data item (sometimes referred to as a column in a table). If an element is not part of an entity, it is called an unattached element.
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Entity |
A group of elements which belong logically together and can be uniquely identified by a key or group of keys (also known as a table).
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Identifying Element |
The element of an entity which uniquely identifies each occurrence of the entity (either on its own or in conjunction with one or more parent keys). For example, Customer Number uniquely identifies each occurrence in the Customer entity. Also called an Identifying Attribute.
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Join Attribute |
An attribute which is used to refer to a joined entity, i.e. as a key in a join relationship (also known as a foreign key). For example, the Customer Number can be a join attribute in the Order entity.
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Join Relationship |
A relationship between two entities such that one or more attributes or keys from one entity can be used to access the second entity. For example, the Order entity has a Join relationship to lookup data in the Customer entity.
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Occurrence |
A single example or instance of an entity (i.e. a row in a table or a record on a file). For example, "Acme Retail Company of Australia" might be an occurrence of Customer.
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Parent Entity |
An entity which owns another entity (the child), i.e. to which the child entity belongs. For example, the Order and Product entities are parents of Ordered Product entity.
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Parent Key |
An identifying element which is used as a key on the parent entity and therefore also on the child entity. For example, Ordered Product entity is a child to the parent Order entity. The key of Order (Order Number) is also a key of Ordered Product.
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Parent Relationship |
A relationship between two entities such that the data in one entity is owned by another entity. For example, the Order entity has a parent relationship to the Ordered Product entity.
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Relationship |
A relationship exists between two entities if, given an occurrence of one entity, it is possible to use data from that entity to access one or more occurrences of the second entity. For example, given an order, it is possible to obtain information about the customer who placed it.
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User View |
A view of the data in an entity. User Views are used to define the keys used to create logical views over the implemented database file. |