By Olin H Bray
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This booklet constitutes a suite of analysis achievements mature adequate to supply a company and trustworthy foundation on modular ontologies. It supplies the reader a close research of the cutting-edge of the learn region and discusses the new ideas, theories and strategies for wisdom modularization.
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Extra resources for Distributed Data-base Management Systems
An attribute will be one of three types (see Figure 2-5): Unique identifier (UID), which uniquely identifies an entity instance. UIDs are implemented as primary keys. Mandatory attributes, which cannot be NULL. 5 Figure 2-5. Entity attributes According to the conventions supported by Barker’s notation: A column name is preceded by a special symbol: # denotes a key attribute * denotes a mandatory attribute o denotes an optional (nonmandatory) attribute Column Name is written with the first letter of each word in uppercase.
This type of recursion is called a hierarchy. Figure 2-9. Example of a one-to-many recursive relationship The recursive relationship in Figure 2-9 may be read as: Each employee may manage one or more employees Each employee may be managed by one and only one employee Implementing one-to-many recursive relationships in DBMS is relatively straightforward. Table 2-1 diagrams a solution by having a foreign key referencing the primary key of the same entity. Table 2-1. Implementing a One-to-Many Recursive Relationship Employee id Name Manager id 1 Joe 2 Tony 1 3 Robert 1 4 Richard 2 5 Jane 2 6 Lisa 3 7 Alex 3 8 Ben 5 9 Mark 5 10 Lan 6 Recursive Many-to-Many Relationships Another type of recursive relationship that is very important in data modeling is the recursive many-to-many (M:N) relationship.
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