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2nd Sem > Information Management - 3 > Flashcards

Information Management - 3 Flashcards

1
Q

Relational model

A

views data logically rather than physically

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2
Q

Table

A
  • Structural and data independence
  • resembles file conceptually
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3
Q

Relational database

A

much easier to understand rather than hierarical and network model

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4
Q

Tables and Their Characteristics

A
  • Logical view if relational database based on relation
  • Table is a two-dimensional structure composed of row and columns
  • Contains group of related entities
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5
Q

Characteristics of Relational Table

A
  1. table is a two-dimensional structure composed of rows and columns
  2. each table row must represent a single entity
  3. each table column must represent an attribute
  4. all values in column must conform a single format
  5. Each row/column intersection represents a data
  6. each column has a specific range of values kniwn attribute domain
  7. order of rows and columns are immaterial on DBMS
  8. each table must have an attribute that uniquely identifies each row
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6
Q

Key

A
  • one or more attribute determines another attribute
  • role is based on determination
    -If you know the value of attribute A, you can determine the value of attribute B
  • **Functional dependence - Attribute B is functionally dependent on A if all rows in table that agree in value for A also agree in value for B
    **
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7
Q

Composite Key

A

composed of one or more attribute

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8
Q

Key Attribute

A

an attribute that is a part of a key

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9
Q

Superkey

A

Any key that uniquely identifies each row

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10
Q

Candidate Key

A

superkey without unnecessary attributes

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11
Q

Null

A

-no data entry
-may composed of:
* missing value
* known but not attribute value
* not applicable condition
-can produce COUNT, SUM, AVERAGE
-create logical problem

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12
Q

Controlled redundancy

A
  • makes relational database work
  • tables within database share common value
  • multiple occurance of values not redundant when required
  • Redundancy exists only when there is unnecessary duplication of attribute values
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13
Q

Foreign Key

A

attribute whose values match primary key

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14
Q

Referential Integrity

A

FK that contains value thatb refers to an existing table row

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15
Q

Secondary Key

A

key used strictly for retrieval purposes

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16
Q

Primary Key

A

candidate key slected to uniquely identify all other attribute values in ant given row

17
Q

Relational Database Keys

A
  1. Superkey
  2. Candidate Key
  3. Primary Key
  4. Foreign Key
  5. Secondary Key
18
Q

Integrity Rules

A
  1. Entity Integrity
  2. Reference Integrity
19
Q

Entity Integrity

A
  • each row will have their own unique identity, foreign key values that can proper reference
  • all primary keys are unique and no null primary key
20
Q

Reference Integrity

A
  • impossible to delete a row in one table whose primary key has mandatory matching foreign key
  • foreign key may have either null entry or entry that matches the primary key
21
Q

Relational Algebra

A
  • theoretical way of manipulating data
  • Use of relational algebra operators on existing relations produces new relations:
    1. Select
    2. Project
    3. Union
    4. Intersect
    5. Difference
    6. Product
    7. DIvide
    8. Join
22
Q

Natural Join

A

selects the rows with common attributes

23
Q

Equijoin

A

links tables based on equality conditionthat compares specific columns

24
Q

Theta Join

A

any other comparison operator used

25
Q

Outer Join

A

any matched data is retained, unmatched data is null

26
Q

Relational Set Operation

A
  1. Relational Algebra
  2. Natural Join
  3. Equijoin
  4. Theta Join
  5. Outer Join
27
Q

Data Dictionary

A
  • provides detailed accounting of all tables found within the user/designer-created database
  • contains attribute names
  • contains metadata
28
Q

Service Catalog

A

data dictionary that descirbes all objects in database

29
Q

Relationships within the Relational Database

A
  1. 1:1 - should be considered as rare in rational database design
  2. 1:M - relational modeling data
    -should be a norm in relational database design
  3. M:N - cannot be implemented in relational database design
    - can be changed to 1:M relationship
30
Q

The 1:M Relationship

A
  • Relational database norm
  • Found in any database environment
31
Q

The 1:1 Relationship

A
  • one entity is related to the other entity and vice versa
  • entity may note be defined properly
  • two identities that belong on the same group
  • conditions required to use
32
Q

M:N Relationship

many to many

A
  • can proude 1:M relationship by breaking it up
  • avoid problems through composite key
    -Includes as foreign keys the primary keys of tables to be linked
33
Q

Data Redundancy Revisited

A
  • data redundancy can lead to data abnormalities
    -Can destroy the effectiveness of the database
  • Foreign Key
    -Control data redundancies by using common attributes shared by tables
    -Crucial to exercising data redundancy control
  • Sometimes, data redundancy is necessary
34
Q

Index

A

orderly arrangement of logically accessed rows in a table

35
Q

Index key

A
  • value reference point
  • point to the location of the identified key
36
Q

Unique index

A

Index in which the index key can have only one pointer value (row) associated with it

37
Q

Each index is associated

A

with only one table

2nd Sem (21 decks)

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