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37 Cards in this Set

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what are the advantages of using DBS over file based systems for data storage?

-control of data redundancy


-preserve data consistency


-sharing of data ( easier )


-improve security


-increase productivity


-support of multiple views of data


- improve maintenance through data independence


-increase concurrency


-improve backup and recovery

what are the disadvantages of using DBS for storing data?

-complexity


-size


-cost of DBMS


-additional hardware costs


-cost of conversion


performance


-overhead for providing generality, security, concurrency control, recovery, and integrity functions


-higher impact of a failure



list the 3 generations of Database Systems?

1 hierarchical/network


2 relational


3 object oriented/object relational

What are the four major issues in databases?

(RISC)


Recovery, Integrity, Security, and Concurrency

What are the advantages of the ANSI-SPACR database architecture?

logical/physical data independence

what is a data model?

a collection of concepts describing data

attribute

A property of an entity or a relationship type

system catalog

a repository of information describing the data in the database. Accessible to all users as well as DBMS

view

defines what is required of a database system from the perspective of a particular job role or enterprise application area

schema

a description of a database.

distributed database

a logically interrelated collection of shared data (and a description of this data) physically distributed over a computer network

SOA

simple object access

web service

a software system designated to support inter-operable machine-to-machine interaction over a network

Integrity constraint

consistency rules that the database is not permitted to violate

Degree

the number of attributes a relation contains

Cardinality

describes the maximum number of possible relationship occurrences for an entity participating in a given relationship type

Cartesian product

a table containing all the possible pairs of rows from 2 tables

Primary key

A candidate key that is selected to uniquely identify each occurrence of an entity type

candidate key

minimal set of attributes that uniquely identifies each occurrence of an entity type

composite key

a candidate key that consists of two or more attributes

foreign key

an attribute, or set of attributes, within one relation that matches the candidate key of some ( possibly the same) relation

define attribute domain

the set of allowable values for one or more attributes

example of attribute domain

number of rooms associated with a property is between 1-15. (the term would be for labeling this range of possible values)

Describe: simple/single-valued attribute

An entity's attribute composed of a single component

Example: simple/ single-valued attribute

Employee with SSN 123-45-6789

Describe: composite attribute

an attribute composed of multiple components, each with an independent existence



Example: composite attribute

Address, Name (can be nested)

Describe: multi-valued attribute

an attribute that holds multiple values for each occurrence of an entity type

Example: multi-valued attribute

Previous jobs for an employee

What is a recursive relationship?

A relationship type where the same entity participates more than once in different roles

What is a Strong Entity type?

Entity type that is not existence-dependent on some other entity type.

What is a Weak Entity type?

Entity type that is existence-dependent on some other entity type.



Identified by a partial key of the weak entity type and by the primary key of the strong entity type they are related to

What is a fan trap?

Where a model represents a relationship between entity types, but pathway between certain entity occurrences is ambiguous

What is a chasm trap?

Where a model suggests the existence of a relationship between entity types, but pathway does not exist between certain entity occurrences

multiplicity

the range of occurrences of an entity per instance of a related entity

Define: Derived attribute

attribute that represents a value that is derivable from value of a related attribute, or set of attributes, not necessarily in the same entity type

Example: Derived attribute

Age derived from DOB and Today's date