basic concepts of databases
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Basic Concepts of DatabasesCST203-2 Database Management Systems
Lecture 2
One Tier ArchitectureEg:
In this scenario, a workgroup database is stored in a shared location on a single machine
Beneficial when we are dealing with data that is relevant to a single user
Client / Server architectureSystem functionality is distributed between
Client moduleServer module
3 tier architectureTo ensure more security and load balancing
for a greater stability
Data modelsA collection of concepts that can be used to describe
the structure of a database
“An integrated collection of concepts for describing data, relationships between data, and constraints on the data.
Database Solutions: A Step-by-step approach to building databases
Include a set of basic operations for specifying retrievals and updates on db
Categories of Data ModelsHigh-level or Conceptual Data models
Low-level or physical data models
Representational or implementation data models
Relational data model Network data model Hierarchical data model
Levels of AbstractionPhysical level describes how a record (e.g.: customer) is stored.
Logical level: describes data stored in database, and the relationships among the data.type customer = recordname : string;street : string;city : integer;end;
View level: application programs hide details of data types. Views can also hide information (e.g., salary) for security purposes.
Data modeling using Entity Relationship model
Database Schema
The logical structure of the database
Eg: the database consists of information about a set of customers and accounts and the relationship between them
Database Instance
The actual content of the database at a particular point in time
Three Schema Architecture
The external schemaDefines one view of data as seen by a specific set of
applications or end users
The conceptual schemaDefines data from perspective of system designerIndependent of end users and data storage mechanism
The internal schemaDefines how data is organized, stored and manipulated in
the application itselfTotally dependent on particular implementation
Data IndependenceLogical Data Independence
Physical Data Independence
EntityRepresents a real world object or concept
Eg: an employee, a project
AttributeRepresents some property of interest that
further describes an entityEg: employee’s name or salary
RelationshipRepresents an association among 2 or more
entitiesEg: an employee works on a project
Example of schema in the entity-relationship model
A Sample Relational Database
Data Definition Language (DDL)Specification notation for defining the database schema
E.g. create table account (
account-number char(10), balance integer)
DBMS have a DDL compiler
Data dictionary contains metadata (i.e., data about data)Database schema Data storage and definition language
language in which the storage structure and access methods used by the database system are specified
Usually an extension of the data definition language
Data Manipulation Language (DML)
Language for accessing and manipulating the data organized by the appropriate data model
DML also known as query language
Two classes of languages Procedural – user specifies what data is required and how
to get those data Nonprocedural – user specifies what data is required
without specifying how to get those data
SQL is the most widely used query language
SQLSQL: widely used non-procedural language
E.g. find the name of the customer with customer-id 192-83-7465select customer.customer-namefrom customerwhere customer.customer-id = ‘192-83-7465’
E.g. find the balances of all accounts held by the customer with customer-id 192-83-7465
select account.balancefrom depositor, accountwhere depositor.customer-id = ‘192-83-7465’ and depositor.account-number = account.account-number
Application programs generally access databases through one of Language extensions to allow embedded SQL Application program interface (e.g. ODBC/JDBC) which allow SQL queries to
be sent to a database
Transaction ManagementA transaction is a collection of operations that performs
a single logical function in a database application
Transaction-management component ensures that the database remains in a consistent (correct) state despite system failures (e.g., power failures and operating system crashes) and transaction failures.
Concurrency-control manager controls the interaction among the concurrent transactions, to ensure the consistency of the database.
Example:Consider a possible interleaving
This is OK. But what about this ???????
T1: A=A+100, B=B-100 T2: A=1.06*A, B=1.06*B
T1: A=A+100, B=B-100 T2: A=1.06*A, B=1.06*B
Storage ManagementStorage manager is a program module that
provides the interface between the low-level data stored in the database and the application programs and queries submitted to the system.
The storage manager is responsible to the following tasks:
Interaction with the file manager Efficient storing, retrieving and updating of data
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