Chapter 1: Introduction

A database-management system

(DBMS) consists of a collection of interrelated data and a collection of programs to access that data. The data describe one particular enterprise.

the architecture of a database system is greatly influenced by the underlying computer system on which the database is running

- centralized. - client-server. - parallel (multi-processor). - distributed.

DBMS

- collection of interrelated data. - set of program to access the data. - an environment that is both convenient & efficient to use.

data models a collection of tools for describing

- data. - data relationships. - data semantics. - data constraints.

data about data like

- database schema. - integrity constraints. - authorization.

alternative way of evaluating a given query

- equivalent expressions. - different algorithms for each operation.

storage manager tasks

- interaction with the file manager. - efficient storing, retrieving & updating of data.

Application programs genrally access database through one of:

- language extensions to allow embedded SQL. - application program interface which allow SQL queries to be sent to a database.

entity relationship model

- models an enterprise as a collection of enitities & relationships. - represented diagrammatically by an enitity-relationship diagram.

older data models

- network model. - hierarchical model.

quary processing

- parsing and tanslation. - optimization. - evaluation.

levels of abstraction

- physical level. - logical level. - view level.

Two classes of query language

- procedural: user specifies what data is required & how to get those data. - declarative: user specifies what data is required without specifies how to get those data.

drawback of using file system to store data

- redundancy & inconsistency. - difficulty in accessing data. - data isolation, multiple files & formats. - integrity problems. - atomicity of updates. - concurrent accesses. - security problems.

data models

- relational model. - entity-relational data model. - object-based data model. - semistructured data model.

storage manage issues

- storage access. - file organization. - indexing and hashing.

database system has several subsystems

- storage manager. - query processor.

SQL

- the most widely used query language. - widely used non-procedural language.

data model

a collection of conceptual tools for describing data, data relationships, data semantics, and data constraints.

storage manager

a program module that provides the interface between the low-level data stored in the database & the application programs and queries submitted to the system.

superkey

a set of one or more attributes that, taken collectively, allow us to identify uniquely a tuple in the relation.

DDL compiler generates

a set of table templates stored in a data dictionary.

Database systems are ubiquitous today

and most people interact, either directly or indirectly, with databases many times every day.

view level

application program hide details of data types for security purposes.

Knowledge-discovery techniques

attempt to discover automatically statistical rules and patterns from data.

The entity-relationship (E-R) datamodel is

awidely used datamodel for database design. It provides a convenient graphical representation to view data, relationships, and constraints.

database applications

banking, airlines, universities, sales, online retailers, manufacturing.

The management of data involves

both the definition of structures for the storage of information and the provision of mechanisms for the manipulation of information.

Database applications are typically

brokenup into a front-end part that runs at client machines and a part that runs at the back end.

Such minimal superkeys are called

candidate keys.

Database systems can be

centralized, or client-server, where one server machine executes work on behalf of multiple client machines.

transaction

collection of operations that performs a single logical function in database application.

The field of data mining

combines knowledge discovery techniques invented by artificial intelligence researchers and statistical analysts, with efficient implementation techniques that enable them to be used on extremely large databases.

concurrency-control manager

controls the interation among the concurrent transactions, to ensure the consistency of the database.

metadata

data about data

logical schema

database design at the logical level.

physical schema

database design at the physical level.

database logical design

deciding on the database schema, database design requires that we find a "good" collection of relation schema.

physical design

deciding on the physical layout of the database.

physical level

describes how a record stored.

logical level

describes the data stored in database, & the relationships among the data.

XML originally intended as

document markup language not database language.

Transaction management

ensures that the database remains in a consistent (correct) state despite system failures. The transaction manager ensures that concurrent transaction executions proceed without conflicting.

transaction management component

ensures that the database remains in consistent (correct) state despite system failures and translation failures.

XML a great way to

exchange data, not just documents.

Database systems can also be designed to

exploit parallel computer architectures.

XML

extensible markup language.

normalization theory

formalize what designs are bad, & test from them.

data-definition language (DDL)

is a language for specifying the database schema and as well as other properties of the data.

data-manipulation language (DML)

is a language that enables users to access or manipulate data.

data manipulation language

language for accessing & manipulating the data organized by the appropriate data model.

data dictionary contains

metadata

XML a wide variety of tools is available for

pasing, browsing & querying XML documents/data.

DML also know as

query language.

referential integrity

references constraint in SQL.

Distributed databases

span multiple geographically separated machines.

data definition language DDL

specification notation for defining the database schema.

Database systems are designed to

store large bodies of information.

query processor

subsystem compiles and executes DDL and DML statements.

storage manager

subsystem provides the interface between the lowlevel data stored in the database and the application programs and queries submitted to the system.

physical data independence

the ability to modify the physical schema without changing the logical schema.

instance

the actual content of the database at a particular point in time.

In three-tier architectures

the back end part is itself broken up into an application server and a database server.

Database design mainly involves

the design of the database schema.

Different types of user interfaces have been designed for

the different types of users.

In two-tier architectures

the front end directly communicates with a database running at the back end.

schema

the logical structure of the data.

The relational datamodel is

the most widely deployed model for storing data in databases. Other data models are the object-oriented model, the object relational model, and semi structured data models.

the database system must provide for

the safety of the information stored, in the face of system crashes or attempts at unauthorized access.

If data are to be shared among several users

the system must avoid possible anomalous results.

The architecture of a database system is greatly influenced by

the underlying computer system on which the database system runs.

prymary key

to denote a candidate key that is chosen by the database designer as the principal means of identifying tuples within a relation.

The primary goal of a DBMS is

to provide an environment that is both convenient and efficient for people to use in retrieving and storing information.

A major purpose of a database system is

to provide users with an abstract view of the data. That is, the system hides certain details of how the data are stored and maintained.

There are four different types of database-system users

way they expect to interact with the system.

business decision

what attributes should we record in the database.

computer science decision

what relation schema should we have & how should the attributes be distributed among the various relation schema.

Nonprocedural DMLs

which require a user to specify only what data are needed, without specifying exactly how to get those data, are widely used today.

XML defined by

www consortium (W3C).