Systems Chapter 3

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Systems Chapter 3
2011-01-27 23:54:47

Chapter 3 Terms
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  1. Entity
    object that exists and wich is distinguishabel frm other objects

    -person, place, object
  2. Entity Type
    defines a collection of entites that have the same attributes

    -Students, radios, cars
  3. Entity Instance
    single item in this collection

    -student with id 123
  4. Entity Set
    set of entity instances; subset of entity type

    - IE students
  5. Attribute
    property or characteristic of an entity type
  6. Simple/Atomic Attribute
    cannot be futher divided into smaller components

  7. Composition attribute
    can be divided into smaller subparts

    • -name: first, last
    • -address: street, city, zip
  8. Single-valued attributed
    has a single value for an entity instance

    -DOB, product weight
  9. Multivalued Attributes
    may have more than one value for an entity instance

    • -Language
    • -Sports played
  10. Derived Attribute
    can be determined by analyzing other attributes

    • -no need to store them in a database
    • -denoted with dashed ellipse
    • -age
  11. Stored Attribute
    attribute whose value cannot be derived from the values of other attributes
  12. Key Attribute
    single attribute or combination of attributes that uniquely identify an individual instance of an entity type

    -Student ID
  13. Maximum Cardinality
    represents the maximum number if unstances of entity B that can be associated with any instance of entity A
  14. Minimum Cardinality
    the minimum number of instances of entity B that must be associated with each instance of entity A
  15. Attribute on a relationship
    stores info related to the relationship
  16. Associative Entity
    an entity type that connects the instances of one or more entity types and contains attributes particular to this assciation

    • -allows us to store data from relationship attributes more effectively
    • -must be many-to-many binary or ternary
  17. Strong Entity Type
    exists independent of other entity types
  18. Weak Entity Type
    depends on another entity type
  19. Superclass
    entity type that has one or more distinct subgroups with unique attributes
  20. Subclass
    entity type that shares common attribtes or relationships distinct from other subclasses
  21. Generalization
    the process of defining general entity types from a set of specialized entity types by identifying their common charactersitics from the bottom up
  22. Speicialization
    is the process of defining one or more subclasses of a superclass by identifying its distinguishing characteristics from the top down
  23. Participation constraints
    dictate if each instance (member) of a superclass must participate as an instance of a subclass
  24. Partial Participation
    an instance of a superclass does not have to be an instance of any of the subclasses
  25. Total participation
    must be an instance of at least one subclass
  26. Disjoint constraints
    define whether it's possible for an instance of a superclass to simultaneously be a member of one or more subclasses
  27. Disjoint Rule
    if an instance oof a superclass is a member of any subclass, then it cannot be a member of more than one subtype
  28. Overlap Rule
    if an instance of a superclass is a member of any subclass, then it can be a member of more than one subtype
  29. Subclass discriminator
    an attribute of a superclass that discriminates a new entry to the superclass into the appropriate subclass
  30. Superclass/Subclass Hierarchy
    is a hierarchical structure of a superclass and its various subclasses in which each subclass has exactly one superclass