cst203-2 database management systems lecture 2. one tier architecture eg: in this scenario, a...
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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
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 Models
High-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.
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
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
Attribute
Represents some property of interest that further describes an entityEg: employee’s name or salary
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 Management
Storage 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