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VA > VA Session 2 ! > Flashcards

VA Session 2 ! Flashcards

1
Q

Interaction with database

A
  • Database
  • DBMS
  • front End Application (= program with easy interface to use (e.g. HR system))
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2
Q

Metadata

A

data that describes structure & properties of data -> proper understanding & use of data

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3
Q

Database metadata

A
  • represents the structure of database
  • Database content that is not the data itself (data about the data)
  • e.g. Names of data structures, data types, data descriptions
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4
Q

Types of databases

A
  1. Transactional = Operational
  2. Analytical
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5
Q

Transactional information

A

collected & used for day-to-day operational needs in organizations

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6
Q

Analytical information

A

collected & used for analytical tasks (based on transactional info)

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7
Q

Operational database

A

collects & presents transactional info in support of daily operational procedures & processes

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8
Q

Analytical database

A

collects & presents analytical info in support of analytical tasks

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9
Q

Use of types of databases

A
  • Typically maintains & uses many operational data sources
  • data warehouse created as separate data store because:
    1. performance of operational day-to-day tasks diminished when competing with analytical queries
    1. structure of database not efficient for operational & analytical purpose
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10
Q

Types of databases: Differences

A
  • Operational Data:
  • time-horizon days / months, detailed, current
  • used by all types of employees, subject oriented
  • small amounts used, high frequency of access, can be updated, non-redundant
  • Analytical Data:
  • time years, summarized (&/or detailed), values over time (snapshots)
  • Used by narrower set of users, application oriented
  • large amounts used, low/modest frequency of access, read & append only, no redundancy
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11
Q

ER modeling

A
  • Entity-relationship
  • conceptual database modeling technique that
  • Organizer & graphically represents
  • the requirements of the collection process
  • good to do before database to know where to put what & not move everything around often
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12
Q

ER diagram (ERD)

A

= result of ER modeling; blueprint of database

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13
Q

Relationship-Types

A
  • One-to-one = one row on one table is connected to one row in other table
  • One-to-many = one row in one table is connected to many rows in other table
  • Many-to-many = many rows in one table are connected to many rows in other table
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14
Q

Cardinality constraints

A

show how many instances of one entity can be associated with instances of another entity

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15
Q

Maximum cardinality

A
  • first
  • One I
  • Many <
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16
Q

II

A
  • One Mandatory
  • 1
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17
Q

I0

A
  • One Optional
  • 1 or 0
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18
Q

> I

A
  • Many Mandatory
  • > = 1
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19
Q

> O

A
  • Many Optional
  • 0, 1 or > 1
20
Q

Relationship attributes

A
  • Sometimes: M:N relationship can have attributes on their own
  • e.g. student (studentID, studentName) >I belongs to with role <I Organization (OrgID, OrgLocation)
21
Q

Relational database model

A
  • represents a database as collection or related tables
22
Q

Column Synonyms

A
  • Attribute
  • Field
23
Q

Relation

A

Table in a relational database:
-1. & 2. each column & row = unique name
- 3. All values in each column must be from the same (predefined) domain & single valued
- 4. order of columns & rows is irrelevant
- 5. + 6. must have (non NAN values) primary key

24
Q

Primary Key

A
  • (set) column whose value is unique for each row
  • Each relation must have one
  • Cannot have 0 values
  • Never changes (e.g. not phone number no primary key)
  • Primary key name = underlined to distinguish from other columns
25
Q

Composite primary key

A

primary key that is composed of multiple columns (only combination of attributes lets row be identify)

26
Q

Entity integrity constraint

A

rule: in a relational table, no primary key column can have null (empty) values

27
Q

Foreign Key

A
  • Column in a relation that refers to primary key column in another (referred) relation
  • Mechanism used to depict relationships in RDMs
    -relational schema: line from foreign key to corresponding primary key
28
Q

Relational schema

A

Visual depiction of relational database model

29
Q

From ER to relational schemas

A
  • Once ERD constructed -> mapped into relational schema (= collection of relations)
  • Each regular entity -> relation
  • Each regular attribute of regular entity -> column of newly created relation
  • If entity has single unique attribute: attribute -> primary key
30
Q

Relational Schema: Mapping entities with composite attributes

A
  • make two columns out of both composite attributes
  • e.g. customer - customerName - 1) customername1, 2) customername2 -> relation / mapped relation = both customernames,
31
Q

Relational Schema: Mapping entities with optional attribute

A
  • make one column of optional & just include existing values
  • e.g. Employee - Bonus (O) -> relation = bonus (0); mapped relation = Bonus, not all rows have values; bonus (O)
32
Q

Relational Schema: Mapping 1:M relationships

A

Relation mapped from entity on M side has a foreign key that
corresponds to primary key of relation mapped from 1 side -> connect by error; attributename (FK)

33
Q

Relational Schema: Mapping M:N relations

A
  • Additional relation created to represent M:N relationship itself
  • 2 foreign keys (corresponding to primary keys of 2 relations representing the 2 entities) -> form the composite primary key of new relation
34
Q

Relational Schema: Mapping 1:1 relationship

A
  • Same as 1:M relations
  • One of mapped relations has foreign key referring to primary key of the other mapped relation (direction not fixed, what fits better)
35
Q

Relational Schema: Referential integrity constraints

A
  • In each row of relation containing a foreign key: value of foreign key either a) matches primary key value or b) is 0
  • Referential integrity constraint lines = lines pointing from foreign to primary key
36
Q

Relational Schema: Mapping candidate keys (= multiple unique attributes): (U)

A
  • Database designer chooses 1 of candidate as primary key
  • Other candidate keys = mapped as non-primary key columns
37
Q

Relational Schema: Mapping multivalued attributes

A
  • Entity containing multivalued attributes: mapped without this attribute
  • separate relation with column representing multivalued an attribute & foreign key column referring to primary key
38
Q

Relational Schema: Mapping 1:M relationship

A

Foreign key must appear in the relation from the M side

39
Q

Multivalued Attribute - definition

A

an attribute that can have >1 value associated with the key of the entity

40
Q

Minimum cardinality

A
  • second
  • Optional O = no relationship necessary
  • Mandatory I = must be at least one relationship
41
Q

Entity

A
  • e.g. table
  • Constructs that represent what database keeps track of (e.g. people, places, items)
  • Basic building block of an ERD
  • Within one ERD each entity must have a different name
42
Q

Differences Foreign & Primary Key

A
  • multiple rows with one foreign key possible but with primary key not
  • multiple foreign keys in one entity possible (not for primary key)
43
Q

Attributes

A
  • characteristics of an entity (column)
  • within one entity: must have different name
44
Q

Unique Attributes

A
  • attributes whose values is different for each entity instance
  • each entity must have at least one
45
Q

Types to visually show database

A
  • Er Model
  • Relational Database Model
  • relational Schema

VA (10 decks)

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