Chapter 10 - arifaiman.files.wordpress.com · 2 2 Chapter 10 - Objectives Main components of an...
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Chapter 10
Database System
Development Lifecycle
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Chapter 10 - Objectives
Main components of an information system.
Main stages of database system development lifecycle.
Main phases of database design: conceptual, logical, and physical design.
Benefits of CASE tools.
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Chapter 10- Objectives
How to evaluate and select a DBMS.
Distinction between data administration and database administration.
Purpose and tasks associated with data administration and database administration.
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Software Depression
Last few decades have seen proliferation of software applications, many requiring constant maintenance involving:– correcting faults,
– implementing new user requirements,
– modifying software to run on new or upgraded platforms.
Effort spent on maintenance began to absorb resources at an alarming rate.
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Software Depression
As a result, many major software projects were
– late,
– over budget,
– unreliable,
– difficult to maintain,
– performed poorly.
In late 1960s, led to ‘software crisis’, now refer to as the ‘software depression’.
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Software Depression
Major reasons for failure of software projects includes:
- lack of a complete requirements specification;
- lack of appropriate development methodology;
- poor decomposition of design into manageable components.
Structured approach to development was proposed called Information Systems Lifecycle (ISLC) / Software Development Lifecycle (SDLC)
Develop database system Database System Lifecycle (DBLC)
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Information Systems Lifecycle:
Information System
Resources that enable collection, management,
control, and dissemination of information
throughout an organization.
Computer-based information system includes
Database, database software, application software,
computer hardware and people/personnel.
Database is fundamental component of IS, and its
development/usage should be viewed from perspective
of the wider requirements of the organization.
Lifecycle of an organization’s IS lifecycle of the
database system
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Database System Development Lifecycle
Database planning
System definition
Requirements collection and analysis
Database design
DBMS selection (optional)
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Database System Development Lifecycle
Application design
Prototyping (optional)
Implementation
Data conversion and loading
Testing
Operational maintenance
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Stages of the Database System Development Lifecycle
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Database Planning
Management activities that allow stages of
database system development lifecycle to be
realized as efficiently and effectively as
possible.
Must be integrated with overall IS strategy of
the organization.
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Database Planning
THREE main issues involved in formulating an IS
strategy:
– Identification of enterprise plans and goals & determine IS
needs
– Evaluation of current IS
– IT opportunities that might yield competitive advantage.
Steps:
– Define the Mission Statement
– Identifying the Mission Objectives
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Database Planning – Mission Statement
Mission statement for the database project defines major aims of database application.
Those driving database project normally define the mission statement.
Mission statement helps clarify purpose of the database project and provides clearer path towards the efficient and effective creation of required database system.
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Database Planning – Mission Objectives
Once mission statement is defined, mission objectives are defined.
Each objective should identify a particular task that the database must support.
May be accompanied by some additional information that specifies the work to be done, the resources with which to do it, and the money to pay for it all.
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Database Planning – Mission Statement &
Objectives
EXAMPLE:
ShowInfo Mission Statement
The purpose of ShowInfo is to maintain show information, allow users
to indicate their presence at a show and view those attending, and to
facitilitate sharing of concert experiences after the show.
ShowInfo Mission Objectives
ShowInfo must maintain data pertinent to attending concerts.
ShowInfo must allow users to indicate shows that they will/might
attend, as well as shows that they have attended in the past.
ShowInfo must allow users to maintain setl ist and concert photo data.
ShowInfo must create reports of future shows.
ShowInfo must archive data about previous shows.
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Database Planning
Database planning should also include development
of standards that govern:
– how data will be collected,
– how the format should be specified,
– what necessary documentation will be needed,
– how design and implementation should proceed.
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System Definition
Describes scope and boundaries of database
system and the major user views.
Included within the scope and boundary of the
database system are the major user views that
are to be supported by the database
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System Definition: User Views
Defines what is required of a database system
from perspective of:
– a particular job role (such as Manager or
Supervisor) or
– enterprise application area (such as
marketing, personnel, or stock control).
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System Definition: User Views
Database application may have one or more
user views.
Identifying user views helps ensure that no
major users of the database are forgotten when
developing requirements for new system.
User views also help in development of complex
database system allowing requirements to be
broken down into manageable pieces.
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System Definition: User Views
Defines what is required of a database system
– Data to be held
– Transactions to be performed on the data
Requirements of a user view
– Distinct to that view
– Overlap with other views
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Representation of a Database System with
Multiple User Views
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Requirements Collection and Analysis
Process of collecting and analyzing information
about the part of organization to be supported
by the database system, and using this
information to identify users’ requirements of
new system.
Involves the collection and analysis of
information part of enterprise to be served
by the database
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Requirements Collection and Analysis
Information is gathered for each major user view including:
– a description of data used or generated;
– details of how data is to be used/generated;
– any additional requirements for new database system.
Information is analyzed to identify requirements to be included in new database system.
Described in the requirements specification. (documents)
Preliminary stage to database designPearson Education © 2009
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Requirements Collection and Analysis
Amount of data gathered:
– Nature of the problem
– Policies of the enterprise
Information collected convert to more structured statement of requirements
Use: Requirements Specification Techniques
– Structured Analysis and Design (SAD)
– Data Flow Diagram (DFD)
– Hierarchical Input Process Output (HIPO)
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Requirements Collection and Analysis
Another important activity is deciding how to
manage the requirements for a database
system with multiple user views.
Three main approaches:
– centralized approach;
– view integration approach;
– combination of both approaches.
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Requirements Collection and Analysis:
Multiple User Views
Centralized/One-Shot approach
– Requirements for each user view are merged
into a single set of requirements.
– A data model is created representing all user
views during the database design stage.
– Preferred when there is significant overlap
in requirements for each user view
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Centralized Approach to Managing
Multiple User Views
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Requirements Collection and Analysis:
Multiple User Views
View integration approach
– Requirements for each user view remain as
separate lists.
– Data models representing each user view are
created and then merged later during the
database design stage.
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Requirements Collection and Analysis:
Multiple User Views
Data model representing single user view (or a
subset of all user views) is called a local data
model.
Each model includes diagrams and
documentation describing requirements for one
or more but not all user views of database.
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Requirements Collection and Analysis:
Multiple User Views
Local data models are then merged at a later
stage during database design to produce a global
data model, which represents all user views for
the database.
Preferred: significant differences between user
views
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View Integration Approach to Managing
Multiple User Views
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Requirements Collection and Analysis:
Multiple User Views
Combination:
– Use both centralized & view integration approaches
– Example:
» Requirements for two or more user views: merged
using centralized approach local logical data
model
» The local logical data model merged with other
model using view integration approach global
logical data model
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Database Design
Process of creating a design for a database that
will support the enterprise’s mission statement
and mission objectives for the required
database system.
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Database Design: Approaches
Main approaches include:
– Top-down
– Bottom-up
– Inside-out
– Mixed
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Database Design
Top-down
– Suitable for complex databases
– Starts with development of data models
– ER model
– Identify entities relationship attributes
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Database Design
Bottom-up
– Begins at the fundamental level of attributes
– Associations between attributes are grouped
into relations that represent types of entities
and relationship between entities
– Appropriate for simple databases with small
number of attributes
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Database Design
Inside-out
– Related to bottom-up
– Identify major entities consider other
entities, r/ships & attributes
Mixed
– Uses both bottom-up & top-down approach
for various parts of the model
– Final combine all parts
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Database Design: Data Modeling
Main purposes of data modeling include:
– to assist in understanding the meaning
(semantics) of the data;
– to facilitate communication about the
information requirements.
Building data model requires answering
questions about entities, relationships, and
attributes.
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Database Design
A data model ensures we understand:
– each user’s perspective of the data;
– nature of the data itself, independent of its physical
representations
– use of data across user views.
Can be used to convey the designer’s understanding of
the information requirements of the enterprise
Support communication between users and designers
ER model
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Criteria to Produce an Optimal Data Model
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Database Design
Three phases of database design:
– Conceptual database design
– Logical database design
– Physical database design.
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Conceptual Database Design
Process of constructing a model of the data
used in an enterprise, independent of all
physical considerations.
Data model is built using the information in
users’ requirements specification.
Throughout the process: model is tested and
validated against the user’s requirements.
Conceptual data model is source of
information for logical design phase.
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Logical Database Design
Process of constructing a model of the data
used in an enterprise based on a specific data
model (e.g. relational), but independent of a
particular DBMS and other physical
considerations.
Conceptual data model is refined and mapped
on to a logical data model.
Logical data model: based on the target data
model for the database (relational data model,
object oriented, etc)
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Logical Database Design
Model tested and validated against the user’s
requirements
– Normalization: test the correctness of a logical data
model
– Ensures the relations derived from data model do
not display data redundancy
– Model should also be examined to ensure it
supports the transactions specified by the users
Logical data model: source of information for
physical database design
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Physical Database Design
Process of producing a description of the
database implementation on secondary storage.
Describes base relations, file organizations, and
indexes used to achieve efficient access to data.
Also describes any associated integrity
constraints and security measures.
Tailored to a specific DBMS system: First
identify the target DBMS
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Physical Database Design
In general: describe HOW we intend to
implement the logical database design.
For relational model:
– Create set of relational tables and constraints on these
tables from the information presented in logical data
model
– Identify specific storage structures and access
methods for the data to achieve optimum
performance for the database system
– Design security protection
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Three-Level ANSI-SPARC Architecture
and Phases of Database Design
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DBMS Selection
Selection of an appropriate DBMS to support the database system.
Undertaken at any time prior to logical design provided sufficient information is available regarding system requirements.
Select a system that meets the current and future requirements of the enterprise, balance against costs.
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DBMS Selection
Main steps to selecting a DBMS:
– define Terms of Reference of study» State the objectives and scope of the study and tasks need to be
undertaken
» Description of the criteria to be used to evaluate the DBMS
» Preliminary list of possible products
» Constraints & timescales for the study
– shortlist two or three products
– evaluate products
– recommend selection and produce report
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DBMS Evaluation Features
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DBMS Evaluation Features
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Example - Evaluation of DBMS Product
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Application Design
Design of user interface and application
programs that use and process the database.
Database design and application design are
parallel activities.
Includes two important activities:
– transaction design;
– user interface design.
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Application Design - Transactions
An action, or series of actions, carried out by a
single user or application program, which
accesses or changes content of the database.
Should define and document the high-level
characteristics of the transactions required.
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Application Design - Transactions
Important characteristics of transactions:
– data to be used by the transaction;
– functional characteristics of the transaction;
– output of the transaction;
– importance to the users;
– expected rate of usage.
Three main types of transactions: retrieval, update, and mixed.
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Prototyping
Building working model of a database system.
Purpose
– to identify features of a system that work well, or are inadequate
– to suggest improvements or even new features
– to clarify the users’ requirements
– to evaluate feasibility of a particular system design.
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Prototyping
Requirements prototyping
– Use prototype to determine requirements
– Requirements complete prototype discarded
Evolutionary prototyping
– Same purpose
– Prototype not discarded further development becomes working database system
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Implementation
Physical realization of the database and application designs.
– Use DDL to create database schemas and empty database files.
– Use DDL to create any specified user views.
– Use 3GL or 4GL to create the application programs. This will include the database transactions implemented using the DML, possibly embedded in a host programming language.
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Data Conversion and Loading
Transferring any existing data into new database and converting any existing applications to run on new database.
Only required when new database system is replacing an old system.
– DBMS normally has utility that loads existing files into new database.
May be possible to convert and use application programs from old system for use by new system.
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Testing
Process of running the database system with the intent of finding errors.
Use carefully planned test strategies and realistic data.
Testing cannot show absence of faults; it can show only that software faults are present.
Demonstrates that database and application programs appear to be working according to requirements.
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Testing
Should also test usability of system.
Evaluation conducted against a usability
specification.
Examples of criteria include:
– Learnability – how long does it take a new user to
become productive with the system?
– Performance – How well does the system response match
the user’s work practice?
– Robustness – How tolerant is the system of user error?
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Testing
– Recoverability – How good is the system at recovering
from user errors?
– Adaptability – How closely is the system tied to a single
model of work?
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Operational Maintenance
Process of monitoring and maintaining database system following installation.
Monitoring performance of system.
– if performance falls, may require tuning or reorganization of the database.
Maintaining and upgrading database application (when required).
Incorporating new requirements into database application.
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CASE (Computer Aided Software
Engineering) Tools
Support provided by CASE tools include:
- data dictionary to store information about
database system’s data;
- design tools to support data analysis;
- tools to permit development of corporate
data model, and conceptual and logical data
models;
- tools to enable prototyping of applications.
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CASE Tools
Provide following benefits:
– Standards - enforce standards
– Integration – store all information generated in repository;
possible to store all data stages of DBLC
– Support for standard methods – simplify the process of
structured techniques documentation correct, more current
– Consistency – all information in the data dictionary
interrelated CASE tools can check its consistency
– Automation - automatically transform parts of a design
spec into executable codes
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CASE Tools and Database System
Development Lifecycle
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Data Administration and Database
Administration
The Data Administrator (DA) and Database
Administrator (DBA) are responsible for
managing and controlling the corporate data
and corporate database, respectively.
DA is more concerned with early stages of
database system development lifecycle and
DBA is more concerned with later stages.
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Data Administration
Management of data resource including:
– database planning,
– development and maintenance of standards,
policies and procedures, and conceptual and
logical database design.
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Database Administration
Management of physical realization of a
database system including:
– physical database design and
implementation,
– setting security and integrity controls,
– monitoring system performance, and
reorganizing the database.
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