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11 Cards in this Set
- Front
- Back
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Hierarchical Model - Overview
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Data are organized into a tree-like structure.
Entity types are related to each other using 1: N mapping, also known as one-to-many relationships. Information is obtained dby traversing the tree. If a one-to-many relationship is violated, then the hierarchy becomes a network. |
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Network Model - Overview
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Permits modeling of many-to-many relationships in data (circuits are added to tree structure)
Set Construct: A set consists of an owner record type, a set name, and a member record type. - A member record type can have that role in more than one set. - An owner record type can also be a member or owner in another set. |
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Relational Model - Overview
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Based on predicate logic and set theory
Avoids the need to write computer programs to express database queries and enforce database integrity constraints. Roughly means "based on tables" |
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Hierarchical Model - Advantages
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Efficient because of embedded structure
High-speed access to large datasets Relationships pre-encoded in structure Queries can be optimized if known in advance |
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Hierarchical Model - Disadvantages
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2-3 stage query, restricted to traversing the hierarchy
Data relationships difficult to modify Not great model for GIS Multiple parents not allowed Must recompile if changes made |
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Network Model - Advantages
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Entity can have multiple parents
Entity can have multiple chldrn Many:Many relationships not allowed but can be handled indirectly in intersection record Stores less redundant info |
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Network Model - Disadvantages
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More extensive linking info must be stored
Real world complex can be stored but at a cost Must recompile if changes made |
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Relational Model - Elaboration
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No hierarchy of data fields
Every data field may be a KEY TUPLES (rows) grouped in 2D tables represent facts A table can now represent relationship among attributes it contains Can JOIN two tables for efficient queries Degree of Relation = # of attributes in a table |
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Relational Model - Advantages
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Flexible, simple structure
Can represent complexity in a relatively redundant-free environment |
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Relational Model - Disadvantages
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More difficult to implement
Slower performance (lack of built in pointers) |
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Hybrid System
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Takes traditional relational table and stores pointers to data to re trieve it at a higher speed.
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