MIS 235 Test 1

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Author:
aidamayy
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239039
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MIS 235 Test 1
Updated:
2013-10-06 14:46:41
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Mote MIS 325 Utexas
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Test 1
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  1. Data model
    • Abstract representation of the date and the associations between them
    • Entity Relationship Model is the most common
  2. Entity
    Also known as table, simple 2D grid of data made of: attributes, fields, columns
  3. Primary Key
    • a non null attribute of set of sttributes that uniqely identifies each instance/row of an entity
    • every entity should have a primary key
  4. simple v. composite primary key
    simple is one word while composite is more than one word
  5. foreign key
    • attribute(s) for a child instance/row of an entity that identifies the unique parent instance/row
    • parents can be in the same or different entity from the child
    • can be null under certain conditions (orphans) 
    • typically the foreign key of a child identifies parent primary key
  6. ER Diagrams
    standardized set of notations for representing entities atrributes, primary keys, foreign keys and relationships between them
  7. degrees of a relationship
    • unary- one entity
    • binary-two entities
    • n-ary- n entities
  8. cardinality of a relationship
    number of records (min and max) in each entity Y that can be associated with each record in X
  9. One to Many Relationship
    • 1:N
    • parent child, each Y with one X 
    • put foreign key in the child that can be associated with each record in X the parent
  10. One to one relationship
    • 1:1
    • spouse relationship
    • put FK in Y to identify X AND define a unique index to eliminate copies
  11. Many to many
    • M:N
    • siblings table
    • create a new associative entity with 2 foreign keys to the associated records in X and Y
  12. Associative Entity
    convert many to many relationship into a new entity consisting of two FKs to the associated records in X and Y
  13. Density of a Many to many relationship
    • actual/possibe
    • associative entity works well with low density
  14. N-ary Relationships
    Create a new associaive entity or super bridge w/ N foreign keys to point to the N sides of the relationships
  15. Normalization
    process of eliminated redundant and inter dep0endent date from a database in order to improve consistency, maintainability, storage, efficiency and scalability
  16. Normalization examples
    • duplicate data is eliminated
    • pre calculated calues are eliminated
    • fewer secondary indives per table
  17. disadvantages to normalization
    more tables, non intuitive, query complexity, slower queries
  18. What to avoid in table making
    • multi value fields (comma deliminated, compud fields, list fields
    • Repeating values
    • compute field
    • multilevel dependencies
  19. Kth Normal Form
    • !NF-all data must be accessible by a primary key, each filed must be scalar (single value), no repeating columns
    • 2NF-every non key field must depends on the entire PK
    • 3NF- every non key field must depends only on the PK
  20. 1NF
    primary key for every table
  21. 2NF
    every non key field must depend on the entire PK
  22. 3NF
    no compound values
  23. denormalization
    • intentionally violating rules to improve performance
    • only do when performance is ciritical
  24. Data definition language
    • Create
    • Alter 
    • Drop
  25. CREATE
    defines new object
  26. ALTER
    modify the definition of an existing object
  27. DROP
    throw away an object
  28. Data Manipulation Language
    • Select
    • Inser
    • Update
    • Delete
  29. SELECT
    answers quations, generates reports, etc
  30. INSERT
    add new records
  31. UPDATE
    modify existing records
  32. DELETE
    throw away records

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