deck_293416 Flashcards
Bit
Smallest unit of data a computer can handle
Byte
Group of bit. Single charactere: letter, number, etc..
Field
Grouping of charactere into a word, a group of words, or a complete number / Columns in a relational DBMS
Record
A group of related fields, such as the student’s name, the course taken, the date, and the grade, it is a row in a relational DBMS
File
A Group of related records / A talbe in a relational DBMS
Database
Def 1: Group of related files Def 2: A collection of data organized to serve many applications efficiently by centralizing the data and managing redundant data
Entity
A person, place, thing, or event about which we store and maintain information
Attribute
Characteristic or quality describing a particular entity
Problems with traditional file environment
- Data redundancy and Inconsistency - Program Data dependance - Lack of flexibility - Poor security - Lack of Data Sharing and Availability
Data Redundancy
The presence of duplicate data in multiple data files so that the same data are stored in more than one place or location
Data Inconsistency
The same attribute may have different values
Program–Data Dependence
The coupling of data stored in files and the specific programs required to update and maintain those files so that changes in programs require changes to the data
Lack of flexibility
A traditional file system can deliver routine scheduled reports after extensive programming efforts, but it cannot deliver ad hoc reports or respond to unanticipated information requirements in a timely fashion
Poor security
Because there is little control or management of data, access to and dissemination of information may be out of control
Database Management System (DBMS)
Software that permits an organization to centralize data, manage them efficiently, and provide access to the stored data by application programs It relieves the programmer or end user from the task of understanding where and how the data are actually stored by separating the logical and physical views of the data
Logical View
Presents data as they would be perceived by end users or business specialists
Physical View
Shows how data are actualy organized and structured on physical storage media
Relational DBMS
Represents data as a 2 dimentiona table called relations
Key Field / Primary Key
A field in a record that uniquely identifies instances of that record so that it can be retrieved, updated, or sorted
Foreign Key
a lookup fi eld to look up data about another relational database
3 Operations of the relational database
- Select - Joint - Project