SFDV2002 - Principles of Information Systems Lecture 5: Designing the Solution.

SFDV2002 - Principles of Information

Systems

Lecture 5:Designing the Solution

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Overview

Setting the contextWhat is the design phase?Key design activitiesLevels of abstraction (reification)Benefits of modellingAn approach: The UML

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# 6 # 5 # 7Tut 3# 8

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Recall Simple Information System

User Interface Data/Processing

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•Here is an example of a building – Guggenheim Museum in Manhatten, New York

•Notes:

•Buildings are not simply built, they are designed first.

•So what tools can be used?

•Like the Civil vs Architecture engineering

This is an example a sketch of the building

This is elevation plan of the ground floor.

Photograph shows Stakeholders, architect and 3D real-world model (from 1945) called a prototype

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Objective: Design solution system

Answers ‘how to do it?’ rather than ‘what to do?’

Main activities:1. Design database 2. Design application3. Design user interfaces4. Design system interfaces5. Create/evolve prototype6. Design system controls

SDLC Review: Design

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Therefore, the aim of the design phase is to translate

the requirements into a buildable solution.

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Key Design Activities

[Adapted: Satzinger et al., 2007]

Activity Question

NetworkHow will the various parts of the system communicate?

ArchitectureHow will each system activity actually be carried out?

User interface(s) How will users interact with the system?

System interfaces

How will the system will work with other systems?

DatabaseHow and where will the system store the information?

PrototypeHave we created prototypes to clarify design decisions?

System controlsCan we be sure that the system will operate correctly and data is secure?

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1.Network: Connecting system components and people with information.

Typically preformed by a specialist such as a network engineer or systems engineer

2.Architecture: Describes how work will actually be carried out by people and computers.

The kind of development environment and eventual deployment platform has a baring on how things work

3.User interfaces: Designed for optimal interactions with system.Recent roles such as usability specialists and human factor

engineers used for this purpose4.System interfaces: Define how system components and system

can communicate with other parts of the system or other systems.

Specify how system will exchange information between different services

5.Database: The underlying schema purposely designed for this system

Lectures 7-9 will look at database in detail6.Prototype: Confirm design choices and elicit feedback.7.System controls: Protect data and ensure system works as it

shouldAuthenticaiton, authorised access and other protection

measures.Design disaster recovery procedures and technology selection

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Levels of Information DesignHigh – Closer to Real World

Low – Closer to Computer rep.

Employee

SalaryEmployee Project Role

Project

Budget

1: Specification

2: ImplementationCREATE TABLE department( dept_code CHAR(4), name VARCHAR2(30) NOT NULL,

PRIMARY KEY (dept_code), UNIQUE (name));

CREATE TABLE employee( emp_id NUMBER(7), firstnames VARCHAR2(50) NOT NULL, surname VARCHAR2(50) NOT NULL, phone VARCHAR2(15), sex CHAR(1) DEFAULT 'F', dept_code CHAR(4) NOT NULL,

PRIMARY KEY (emp_id), FOREIGN KEY (dept_code) REFERENCES department );

CREATE TABLE department( dept_code CHAR(4), name VARCHAR2(30) NOT NULL,

PRIMARY KEY (dept_code), UNIQUE (name));

Ab

stra

ctio

n s

pect

rum

Conceptual

Logical

Physical

Business

System

Technology

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1- Conceptual design:As close to the real world as possible documenting the real world (ERDS, class diagrams etc.)Attempts to abstract or represent real-world information and relationships from domainEntirely independent of implementation concerns (i.e., No concern for the type of database to store resulting data)

2 - Logical design:More closely associated with documenting the real world in terms of corresponding, typically relational database structures (more specific). Specification:

Applied to generic database solutionData model but not technology dependent

Implementation:Technology chosen and database transformed to meet requirements of technology

3 - Physical design:Physical storage within the databaseRecords, pointers, tracks, sectors, etc.As we will see handled by the DBMS and invisible to users.

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Why use Models for Design?Able to represent complex phenomena through

abstractionRepresent intangible aspects of a system A method of documenting the proposed systemAn opportunity to clarify and refine designImprove communication between stakeholdersProvide documentation for future maintenanceAdd rigor to a project when used with CASE

tools

Approaches: Miniature replicas, Virtual 3D models (paper, wood, clay, wax, …), Blueprints, Diagrams on paper and Electronic designs

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Modeling

[Source: Stair and Reynolds, 2003]

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Recall Source Documents[S

ource

: Satzin

ger e

t al., 2

00

4]

CUSTOMERADDRESS

PRODUCTORDER DETAIL

ORDER DETAIL

PAYMENT

ORDER HEAD

ORDER HEAD

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Resulting Conceptual Design

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What Does Unified Mean?

Across historical methods and notationsAcross the development lifecycleAcross application domainsAcross implementation languages and

platformsAcross development processesAcross internal concepts

[Source: Rumbaugh et al., 2005]

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Example UML Diagrams

Class

Collaboration

Use Case

State Machine

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Example UML Diagrams (cont’)

Activity

Sequence

Package

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ClassShows Structure of system.

Collaboration:Highlights how different parts of the system interact

State machine: Represents potential life histories of an object of a class. (lifetime)

Use Case:Models the functionality of the proposed system as perceived by people or things that interact with the systemA use case itself is effectively a unit of functionality.

Activity:Represents the flow of control for performing some task or computationCould tie to a Use Case diagram

Sequence:Shows a set of message calls between objects over a time period

Package: A way to organise models themselves by grouping in some way.

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Summary

The design phase is concerned with how the solution will implement the requirements

Encompasses the transition from the requirements specification to the system blueprints

A variety of modelling approaches can be employed to visualise different aspects of the proposed system

The UML is a collection of inter-related diagramming notations for use primarily in design and analysis