dbms models

DATABASE MANAGEMENT SYSTEM

Data Model & Database Models

Course Instructor: Munawar Ahmad

Plan Executor

OptimizerOperator Evaluator

ParserSQL Engine

Recovery Manager

LockManager

TxManager

Files & Access

Buffer Manager

Disk Space Manager DBMS

CatalogData File Database

Web Forms Front-EndSQL I/f

SQL Commands

DBMS Architecture

People Who Work with Databases

Database Implementers/ Designers

DBA

Application Programmers

End Users

End Users Casual users

These are people who use the database occasionally. Naive users

These are users who constantly querying and updating the database.

Eg. Reservation Clerks of Airline, Railway, Hotel, etc.

Clerks at receiving station of Courier service, Insurance agencies, etc.

Sophisticated Users

People who use for their complex requirements.

Eg. Engineers, Scientists, Business analysts… Standalone Users

Who maintain database for personal use.

DBA

Managing resources

Creation of user accounts

Providing security and authorization

Managing poor system response time

System Recovery

Tuning the Database

Various types of data: Images, Text, complex queries, Data Mining, etc.

Enterprise Resource Planning (ERP) Management Resource Planning (MRP) Database in Web technologies Banking: all transactions Airlines: reservations, schedules Universities: registration, gradesCurrent Database trends: Multimedia databases Interactive video Streaming data Digital Libraries Databases touch all aspects of our lives

Applications of DBMS

Data Model Overview

• What is data model ?• Why data models are important ?• Basic data-modeling building blocks.• What are business rules and how do they

influence database design?• How the major data models evolved ?• How data models can be classified by level of

abstraction ?

What is Data Model

• Data Model: A set of concepts to describe the structure of a database, and certain constraints that the database should obey.

• Data Model Operations: Operations for specifying database retrievals and updates by referring to the concepts of the data model. Operations on the data model may include basic operations and user-defined operations.

Data Model Basic Building Blocks

• Entity– Anything about which data will be collected/stored

• Attribute– Characteristic of an entity

• Relationship– Describes an association among entities

• One-to-one (1:1) relationship• One-to-many (1:M) relationship • Many-to-many (M:N or M:M) relationship

• Constraint– A restriction placed on the data

Importance of Data Models

Data models Representations, usually graphical, of complex

real-world data structures Facilitate interaction among the designer, the

applications programmer and the end user End-users have different views and needs

for data Data model organizes data for various users

Business Rules

• Brief, precise and unambiguous descriptions of policies, procedures or principles within the organization

• Apply to any organization that stores and uses data to generate information

• Description of operations that help to create and enforce actions within that organization’s environment

The Evolution of Data Models

Categories of data models

• Conceptual (high-level, semantic) data models: Provide concepts that are close to the way many users perceive data. (Also called entity-based or object-based data models.)

• Physical (low-level, internal) data models: Provide concepts that describe details of how data is stored in the computer.

• Implementation (representational/External) data models: Provide concepts that fall between the above two, balancing user views with some computer storage details.

Degrees of Data Abstraction American National Standards

Institute (ANSI) Standards Planning and

Requirements Committee (SPARC)

Developed standards 1970 Framework for data

modeling based on degrees of data abstraction:

External Conceptual Internal Physical

The External Model

Each end users’ view of the data environment Modeler subdivides requirements and constraints into

functional (Business unit’s) modules These can be examined within the framework of their external

models

External Model – Advantages

• Easy to identify specific data required to support each business unit’s operations

• Facilitates designer’s job by providing feedback about the model’s adequacy

• Creation of external models helps to identify and ensure security constraints in the database design

• Simplifies application program development

The Conceptual Model

• Global view of the entire database• Representation of data as viewed by the entire organization• Basis for identification and high-level description of main

data objects, avoiding details

The Conceptual Model• Software and hardware independent

– Independent of DBMS software– Independent of hardware to be used– Changes in either hardware or DBMS

software have no effect on the database design at the conceptual level

• Most widely used conceptual model is the Entity Relationship (ER) model– Provides a relatively easily understood

macro level view of data environment

The Internal Model

• The database as “seen” by the DBMS• Maps the conceptual model to the DBMS• Depicts a specific representation of an internal model• Logical independence

– Can change the internal model without affecting the conceptual model

The Physical Model

• Lowest level of abstraction– Describes the way data are saved on

storage media such as disks or tapes

• Software and hardware dependent– Requires database designers to have a

detailed knowledge of the hardware and software used to implement database design

• Physical independence – Can change the physical model without

affecting the internal model

Degrees of Data Abstraction - Summary

Hierarchical DB model

• Logically represented by an upside down TREE• Each parent can have many children• Each child has only one parent• The top layer is perceived as the parent of the

segment directly beneath it.• The segments below other segments are the children

of the segment above them.

SALIENT FEATURES

Hierarchical DB model

Example

Emp No. First Name Last Name Dept Num

100 John Dougals 2A

101 Antony Wanton 2B

102 Mary Queen 2C

103 David Moorey 2D

Serial No. Type User Emp No.

3009734-4 Computer 100

3-23-283742 Monitor 100

2-22-723423 Monitor 100

232342 Printer 100

PARENT

CHILD

Advantages

• Conceptual simplicity

• Data independence

• Efficiency dealing with a large database

Disadvantages• Complex implementation

• Difficult to manage and lack of standards

• Lacks structural independence

• Applications programming and use complexity

• Implementation limitations (no M:N relationship)

Network DB model

Network DB model• Developed in mid 1960s as part of work of CODASYL

(Conference on Data Systems Languages) which proposed programming language COBOL (1966) and then network model (1971)

• The network model has greater flexibility than the hierarchical model for handling complex spatial relationships

• Objective of network model is to separate data structure from physical storage, eliminate unnecessary duplication of data with associated errors and costs

• The Network Database Model was created for three main purposes :

- representing a complex data relationship more effectively

- improving database performance- imposing a database standard

Network DB model

• Major characteristic of this database model is that it comprises of at least two record types ; the owner & the member.

• An owner is a record type equivalent to the parent type in the hierarchal database model, and the member record type resembles the child type in the hierarchal model.

• The network database model uses a data management language that defines data characteristics and the data structure in order to manipulate the data.

Network DB model• The network model contains logical information such as

connectivity relationships among nodes and links, directions of links, and costs of nodes and links.

• Example with diagram

Key terms in network Model• A node represents an object of interest.• A link represents a relationship between two nodes. Within a

directed network, any link can be bidirected (that is, able to be traversed either from the start node to the end node or from the end node to the start node) or unidirected (that is, able to be traversed only from the start node to the end node). Within an undirected network, all links are bidirected.

• A path is an alternating sequence of nodes and links, beginning and ending with nodes, and usually with no nodes and links appearing more than once. (Repeating nodes and links within a path are permitted, but are rare in most network applications.)

Key terms in network Model

• A network is a set of nodes and links. A network is directed if the links that it contains are directed, and a network is undirected if the links that it contains are undirected.

• A logical network contains connectivity information but no geometric information. This is the model used for network analysis. A logical network can be treated as a directed graph or undirected graph, depending on the application.

• Cost is a non-negative numeric attribute that can be associated with links or nodes for computing the minimum cost path

• Duration is a non-negative numeric attribute that can be associated with links or nodes to specify a duration value for the link or node.

Network Hierarchy

• A network hierarchy enables us to represent a network with multiple levels of abstraction by assigning a hierarchy level to each node.

• The lowest (most detailed) level in the hierarchy is level 1, and successive higher levels are numbered 2, 3, and so on.

• Nodes at adjacent levels of a network hierarchy have parent-child relationships.

• Each node at the higher level can be the parent node for one or more nodes at the lower level.

Network Hierarchy

• Each node at the lower level can be a child node of one node at the higher level.

• Sibling nodes are nodes that have the same parent node.

• Links can also have parent-child relationships. However, because links are not assigned to a hierarchy level, there is not necessarily a relationship between link parent-child relationships and network hierarchy levels.

• Sibling links are links that have the same parent link.

Applications of Network Model

• In a typical road network, the intersections of roads are nodes and the road segments between two intersections are links. An important operation with a road network is to find the path from a start point to an end point, minimizing either the travel time or distance. There may be additional constraints on the path computation, such as having the path go through a particular landmark or avoid a particular intersection.

• Also in a biochemical process metabolic pathways are networks involved in enzymatic reactions, while regulatory pathways represent protein-protein interactions. In this example, a pathway is a network; genes, proteins, and chemical compounds are nodes; and reactions among nodes are links.

Applications of Network Model

• The subway network of any major city is probably best modeled as a logical network, assuming that precise spatial representation of the stops and track lines is unimportant. Important operations with a train network include finding all stations that can be reached from a specified station, finding the number of stops between two specified stations, and finding the travel time between two stations.

Advantages

• Simplicity : The network model is conceptually simple and easy to design.

• Ability to handle more relationship types : The network model can handle the one-to-many and many-to-many relationships.

• Ease of data access : In the network database terminology, a relationship is a set. Each set comprises of two types of records.- an owner record and a member record, In a network model an application can access an owner record and all the member records within a set.

Advantages

• Data Integrity : In a network model, no member can exist without an owner. A user must therefore first define the owner record and then the member record. This ensures the integrity.

• Data Independence : The network model draws a clear line of demarcation between programs and the complex physical storage details. The application programs work independently of the data. Any changes made in the data characteristics do not affect the application program.

Disadvantages

• System Complexity : The structure of the network model is very difficult to change. This type of system is very complex

• Lack of Structural independence : This model lacks structural independence. This database model should be used when it is necessary to have a flexible way of representing objects and their relationship. Any changes made to the database structure require the application programs to be modified before they can access data.

Relational DB model

Why Study the Relational Model? • Most widely used model.

– Vendors: IBM, Informix, Microsoft, Oracle, Sybase, etc.

• “Legacy systems” in older models – E.G., IBM’s IMS

• Recent competitor: object-oriented model – ObjectStore, Versant, Ontos– A synthesis emerging: object-relational model

• Informix Universal Server, UniSQL, O2, Oracle, DB2

DefinitionsInstance

A database instance, or an ‘instance’ is made up of the background processes needed by the database software.

Include a process monitor, session monitor, lock monitor, etc. They will vary from database vendor to database vendor.

DefinitionsWhat is a schema?

A SCHEMA IS NOT A DATABASE, AND A DATABASE IS NOT A SCHEMA.

A database instance controls 0 or more databases. A database contains 0 or more database application schemas.A database application schema

Set of database objects that apply to a specific application. Objects are relational in nature, and are related to each other, within a database to serve a

specific functionality. Example payroll, purchasing, calibration, trigger, etc. A database application schema not a database. Usually several schemas coexist in a

database.

A database application is the code base to manipulate and retrieve the data stored in the database application schema.

Definitions Cont.Primary Definitions

• Table, a set of columns that contain data. In the old days, a table was called a file.

• Row, a set of columns from a table reflecting a record.

• Index, an object that allows for fast retrieval of table rows. Every primary key and foreign key should have an index for retrieval speed.

• Primary key, often designated pk, is 1 or more columns in a table that makes a record unique.


• Foreign key, often designated fk, is a common column common between 2 tables that define the relationship between those 2 tables.

• Foreign keys are either mandatory or optional. Mandatory forces a child to have a parent by creating a not null column at the child. Optional allows a child to exist without a parent, allowing a nullable column at the child table (not a common circumstance).


Entity Relationship Diagram or ER is a pictorial representation of the application schema.

Index_no


Constraints are rules residing in the database’s data dictionary governing relationships and dictating the ways records are manipulated, what is a legal move vs. what is an illegal move.

These are of the utmost importance for a secure and consistent set of data.


Data Manipulation Language or DML, sql statements that insert, update or delete database in a database.

Data Definition Language or DDL, sql used to create and modify database objects used in an application schema.


A transaction is a logical unit of work that contains one or more SQL statements. A transaction is an atomic unit. The effects of all the SQL statements in a

transaction can be either all committed (applied to the database) or all rolled back (undone from the database), insuring data consistency.


• A view is a selective presentation of the structure of, and data in, one or more tables (or other views).

• A view is a ‘virtual table’, having predefined columns and joins to one or more tables, reflecting a specific facet of information.


Database triggers are PL/SQL, Java, or C procedures that run implicitly whenever a table or view is modified or when some user actions or database system actions occur. Database triggers can be used in a variety of ways for

managing your database. For example, they can automate data generation, audit data

modifications, enforce complex integrity constraints, and customize complex security authorizations.

Trigger methodology differs between databases.

Terminology

Name Price Category Manufacturer

gizmo $19.99 gadgets GizmoWorks

Power gizmo $29.99 gadgets GizmoWorks

SingleTouch $149.99 photography Canon

MultiTouch $203.99 household Hitachi

Tuples or rows or records

Attribute namesTable name or relation name

Products:

Relational DB model

Relation subject to the following rules

• Relation (file, table) is a two-dimensional table. • Attribute (i.e. field or data item) is a column in the

table. • Each column in the table has a unique name within

that table. • Each column is homogeneous. Thus the entries in any

column are all of the same type (e.g. age, name, employee-number, etc).

• Each column has a domain, the set of possible values that can appear in that column.

• A Tuple (i.e. record) is a row in the table.

Relation subject to the following rules

• The order of the rows and columns is not important. • Values of a row all relate to some thing or portion of a thing. • Repeating groups (collections of logically related attributes

that occur multiple times within one record occurrence) are not allowed.

• Duplicate rows are not allowed (candidate keys are designed to prevent this).

• Cells must be single-valued (but can be variable length). Single valued means the following: – Cannot contain multiple values such as 'A1,B2,C3'. – Cannot contain combined values such as 'ABC-XYZ' where

'ABC' means one thing and 'XYZ' another

Thank You

dbms models

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