Chapter1 Flashcards
What is database management system ?
Is a collection of interrelated data and set of programs to access those data
What is the primary goal of DBMS
Is to provide a way to store and retrieve database information that is both convenient and efficient
What is major purpose of database system
To provide users with an abstract view of data (systems hides certain details)
What are the levels of abstraction.
Physical level.
Logical level
View level
What is physical level
Is the lowest level of abstraction describing how data are stored. Describe complex low level data structures in detail
What is logical level
Is the level that describes what data are stored in the database and what relationships exist among those data
What level of abstraction does the data administrator decides what info to keep in the database ?
Logical level of abstraction
What is View level
Is the highest level of abstraction that describes only part of the entire database
What is schema ?
Is the overall design of the database
What is an instance?
Is the collection of info that are stored in the database at a particular moment
The ability to modify the physical without changing the logical schema is called?
Physical data independence
Mention classification of data models
Relational
Entity relational
Object based data model
Semistructure data model
What is relational model
Uses collection of tables to represent both data and the relationships among those data
What is entity relationship model
Uses collection of basic objects called entities and relationships among those objects
What is object based data model
Extended the entity relationship with encapsulation , method and object identitity
What is semstructured data model
Permits the specification of data where individuals data items of the same type may have different sets of attributes
What is database manipulation lang
Is a lng that enables users to access or manipulate data as organised by the appropriate data model
Types of data base manipulation lang
Procedural and non procedural
What is a procedural and non procedural
Procedural DBML requires a user to specify what data are needed and how to get them while non procedural requires a user to specify what data are needed without specifying how to get those data
What is data base definition lang
Is a lang that is used in the definition of database schema
What is a super key
Is a set of one or more attributes that taken collectively allow us to identify uniquely a tuple in the relation
What is relational algebra
It consists of set of operations that takes one or two relations as input and produce a new relation as their result
Mention six basic operators
Project
Select
Cartisian product
Set difference
Union
Rename
