introduction to information systems analysis systems design application architecture & modeling

INFO 503 Lecture #5 1

Introduction to InformationSystems Analysis

Systems DesignApplication Architecture & Modeling

INFO 503

Glenn Booker


System Design

• System Design (a.k.a. physical design) includes the evaluation of alternative solutions, and specification of a detailed solution

• Focus is the shift from logical to physical design; now technology counts!

• Critical to consider off-the-shelf options


Design Strategies

• Modern structured design

• Information engineering

• Prototyping

• Object-Oriented Design (OOD)

• Joint Application Development (JAD)

• Rapid Application Development (RAD)


Modern Structured Design

• A.k.a. top-down program design and structured programming

• Is a process-oriented technique to break a program into smaller pieces (modules) by using certain rules and guidelines

• Each module is a set of instructions to perform a specific function


Modern Structured Design

• Modules should be cohesive - perform only one function; this helps reusability too

• Modules should be loosely coupled - have minimal interaction or dependency on each other

• Capture design in a structure chart, p. 474 (314)

• Not event driven or object-oriented


Information Engineering

• Analysis was based on defining applications to support the requirements of various business areas

• IE does not have its own unique design technique; tools such as the ERD are the starting point– Address process issues later


Prototyping

• Developing prototypes: – Encourages end user involvement– Is well suited to iterative development– Allows hands-on verification of requirements– Provides quick feedback– Often speeds several life cycle phases


Prototyping

• But prototyping:– Encourages irresponsible code-and-fix

life cycle– Can only augment paper specifications

and other design techniques– Omits several design issues; storage,

control, performance


Prototyping

• And prototyping:– Can lead to premature design commitment

(lock in design options)– Can reduce creativity– Can lead to feature (scope) creep– Can result in slower performance


Object-Oriented Design

• OOD uses the results of OOA to design objects which will implement the system

• Addresses data and process issues at the same time

• Can, for example, focus on defining objects, and then defining the methods which communicate between them, p. 478 (546)


Joint Application Development

• JAD can be used for participative development of a design, in conjunction with other design techniques


Rapid Application Development

• RAD blends other design techniques (structured design, information engineering, prototyping and JAD) to speed system development

• Often based on using specific tools which support the process


FAST Design Methodology

• Design covers the following FAST phases:– Decision Analysis (Configuration) Phase,

from Chapter 5 in the 6th edition– Procurement Phase (not a separate phase,

it is addressed during System Design phase in the 6th edition)

– Physical Design and Integration Phase, this is detailed design before construction of the system


Decision Analysis (Configuration) Phase

• The decision analysis phase identifies candidate configurations, and picks the best

• Activities are:– 5.1 Identify Candidate Solutions– 5.2 Analyze Candidate Solutions– 5.3 Compare Candidate Solutions– 5.4 Update the Project Plan– 5.5 Recommend a System Solution


Identify Candidate Solutions

• This activity identifies the candidate system design solutions, based on business needs and possible implementation technology

• Ideas may come from system owners, users, and others involved in the analysis effort

• Candidates may be based on the technology architecture of your organization


Identify Candidate Solutions

• Activity consists largely of brainstorming for ideas, followed by research to assess their characteristics

• Do not judge the solutions - yet

• Output is a table to describe possible solutions, p. 221 (322), the Candidate Systems Matrix


Analyze Candidate Solutions

• Now assess each candidate solution for:– Technical feasibility (practical and staffable)– Operational feasibility (effect on users)– Economic feasibility (is it cost effective?)– Schedule feasibility (can it be done on time?)

• Need to define hardware, training, and software costs for each solution

• Output: feasibility assessment, p. 223 (324)


Compare Candidate Solutions

• Based on the relative importance of the feasibility criteria (i.e. their weight in %), score each of the candidate solutions– Weighting of feasibility criteria often done by

the system owner– Throw out infeasible solutions (those which

are impossible)

• Pick the best solution!


Update the Project Plan

Does this task seem familiar yet?

• Update the project plan to reflect the chosen system configuration

• Reevaluate scope and tasks as needed


Recommend a System Solution

• Now use the updated project plan to recommend a solution to the system owner, with other key interested parties present– Might give recommendations (the system

proposal) verbally or in writing– Salesmanship is often helpful to pitch

the solution

• Hopefully ends with approval to continue


Procurement Phase

• The procurement phase is to assess off-the-shelf options for supporting system design

• This phase is a blend of two new tasks for the “Procurement phase,” and three revised tasks for the “Decision Analysis phase”– Task numbering in the 6th edition looks weird;

it’s intended to replace the specified steps in phases 4 and 5, respectively

p. 487 (326)


Procurement Phase

• New tasks for the Procurement phase are:– 4.1 Research Technical Criteria and Options– 4.2 Solicit Proposals from Vendors

• Revised Decision Analysis phase tasks:– 5A.1 Validate Vendor Claims and Performance– 5A.2 Evaluate and Rank Vendor Proposals– 5A.3 Award Contract and Debrief Vendors


Research Technical Criteria and Options

• Identify specifications for hardware and software - functions, features, and critical performance needs - based on the system requirements– May be based on internal standards, and

research of trade journals and magazines

• Use to define technical criteria, product options, and potential vendors


Solicit Proposals from Vendors

• Based on the technical criteria, prepare a request for quotation (RFQ) or arequest for proposal (RFP)– An RFQ is used for a predefined product– Use an RFP when the product is ill defined

• The RFQ/RFP must define the selection criteria, and classify requirements as mandatory, essential, or optional


Validate Vendor Claims and Performance

• Proposals from prospective vendors must be validated to ensure their individual merits– For major software proposals, a Software

Capability Evaluation (SCE) may be used

• Validation may be through site visits, contacting other clients, and other research

• Results in validated or invalidated proposals– ‘Invalidated’ means you don’t believe them


Evaluate and Rank Vendor Proposals

• Throw out all invalidated proposals

• Validated proposals can now be evaluated and ranked, using the predefined criteria– This is a form of feasibility assessment, but it

might include criteria about the stability of the vendor, or their level of support

• Results in a recommendation to use a particular vendor (we hope)


Award Contract and Debrief Vendors

• The vendor selection is approved by management or the system owner

• Contracts are prepared, negotiated, and reviewed by winning vendor and system owner

• All candidate vendors are briefed on the results of the evaluation (if you’re nice)

• Update affected interface requirements


Physical Design & Integration Phase

• This phase bridges the gulf between the user requirements and the builders’ input needs– 6.1 Design the Application Architecture– 6.2 Design the System Database– 6.3 Design the System Interface– 6.4 Package Design Specifications– 6.5 Update Project Plan


Design the Application Architecture

• Defines technologies used by the system, including data, process, interface, and network components

• How will data, process, and interface be distributed across locations?– Based on data and process models

• Might include physical data flow diagram, p. 482 (373)


Design the System Database

• System database(s) are designed in more detail – allowing not only for full 3NF, but also addressing performance, design flexibility, storage, security, record size, and backup/recovery needs

• Capture in a database schema (often ERD)


Design the System Interface

• Design the user interfaces to the system – inputs and outputs

• Design preprinted forms and reports

• Lots of existing user input is helpful!

• Consider ease of learning, as well as use

• Define controls to help get complete and correct data (minimize input errors)


Package Design Specifications

• Take the results of the previous three steps and put it into a design specification document – essentially a blueprint to guide the system builders

• Need to balance how much design must be specified for the builders, and how much can be left to their discretion and creativity

• Review with all affected parties


Update Project Plan

Mary had a little lambWhose fleece was white as snowAnd everywhere that Mary went

She updated the project plan to reflect her progress

• Update the project plan, now that full design information is available (last sanity check before the start of construction!)


Application Architecture

• Return to general design focus, not detailed• Application architecture addresses general

system design and technology issues:– How distributed is computing (processing)?– How distributed is data storage?– Make or buy technology? – Which technologies are used for user and

system interfaces, and for programming?


Modeling Application Architecture

• Application architectures can be captured in many ways

• A physical data flow diagram (PDFD) can show the technical design, such as the software or people involved in each process– Physical data flows can identify both the name

of each data flow, and how it is implemented (person’s role, bar code, HTML, VB, etc.)



• Physical data flows expand on the logical model; may also show user vs machine lines

• Physical data flows may include:– Input or output to/from a process– Database commands (CRUD) with data stores– Import or export of data from another system– Flow of data between two modules or

subsystems within your system

p. 504 (373)



• Physical data stores might include:– An entire database– A table in a database– A file on the computer (whether temporary

or permanent)– A tape backup device– Any other kind of file, paper, or form



• A network topology data flow diagram can show which processors or people support various processes

• System flowcharts were popular for showing all programs, inputs, outputs, data, and processes at once - whew!

• CASE tools can automate generation of flowcharts and DFDs


IT Architecture

• IT architecture is evolving rapidly; stay tuned for current events! (see SEI, ACM)

• Networking architecture issues drive many others, so look at them first– Historic footnote: early PCs weren’t designed

for multiple users or local networks

• Wireless communications emerging as newest key factor in networking


Five Application Layers

• Presentation layer is what the user sees

• Presentation logic layer determines what needs to be displayed on the screen

• Application logic layer controls how the application runs

• Data manipulation layer controls getting data, which lives in the data layer


IT Architecture

• Architecture options range from centralized to distributed in varying degrees– Purely centralized computing was the

mainframe philosophy (one box does it all)– Web-based systems are the most decentralized

• “Servers” are computers shared by many users at once

• “Clients” are used by one user at a time


IT Architecture

• Servers might fulfill many purposes– File servers hold data files used by many users– Database servers run the database program and

store its data– Application servers get data inputs from the

clients, and get data from the database server– Web servers host a web site, and communicate

among clients and application servers


IT Architecture

• Clients can be ‘fat’ or ‘thin’– Fat clients have a custom application installed

to communicate with the servers (now rare)• If you had to install a special program to use that

system, you are probably using a fat client

– Thin clients communicate with the servers through an ordinary (not customized) program, such as a web browser (now common)

• Thin clients act like a dumb terminal


IT Architecture

• Architecture options (see p. 511 (355)) are:– Centralized computing (not shown)– File server architecture– Distributed presentation (2 tier)– Distributed data (2 tier)– Distributed data & application (n tier)– Network computing (web)


Centralized Computing

• Centralized computing was the only architecture approach through the 1970’s

• Used a mainframe or minicomputer to do all the work, accessed through terminals– VT100 or IBM 3270 terminals; really dumb

clients, they only displayed what text the mainframe sent to them

• Very few systems still use this


File Server Architecture

• This primitive form of distributed computing stores data on a file server, and everything else is done by the clients

• The file server just holds the shared data files and lets the clients read it or write to it when needed

• Is a common cheap way to share data across a local area network (LAN)


Client/server Architecture

• Client/server architecture (distributed or cooperative computing) is the dominant network architecture starting in the 1980’s

• Data, software, and interfaces may be distributed across many clients and servers– ‘Distributed presentation’, ‘distributed data’,

and ‘distributed data and application’ structures are all types of client/server architecture


Server Types

• Client/server may use many server types– Database server for data and data manipulation– Transaction server to control groups of business

transactions together– Application server for the same layer– Messaging or groupware for Notes or Exchange– Web server for hosting Internet or Intranet sites


Distributed Presentation

• Distributed presentation (a.k.a. chintzy client/server) puts a pretty GUI on what were text-based (character user interface, or CUI) terminal screens– May use CASE tool called a screen scraper to

generate a quick GUI from a CUI– Client does presentation and pres. logic layers

• Still is fundamentally centralized computing


Distributed Data

• Distributed data (two-tier client/server) puts stored data on the server, and business logic and user interfaces on the clients– A local or wide area network (LAN or WAN)

connects clients and servers– Reduces network traffic compared to file server

architecture; easier to maintain data integrity– This is classic 1980’s client/server design


Distributed Data and Application

• Also called three-tiered or n-tiered client/server, this distributes data and application logic to separate servers– Adds an application or transaction server

to monitor transactions & handle application logic functions

– Client still handles presentation and pres. logic– Is relatively new but increasingly common


Network Computing

• Network computing distributes presentation logic to web servers, while web browsers handle only the presentation layer– Otherwise looks the same as n-tier client/server– Is the foundation for most e-commerce systems

• Maintaining security is a major challenge• Emerging as foundation for widely

distributed computing and data structures


Data Architecture

• Relational databases are the most common tool used across distributed data architecture

• The database engine is what handles data– Data may be distributed across servers– One table may be partitioned vertically (fields)

or horizontally (records) across several servers– Data may be replicated across servers, too


Interface Architecture

• Many options exist for handling interfaces

• Batch input and output is used to handle a large group of transactions at once

• On-line processing handles transactions as needed

• Remote batch processing handles a batch somewhere else; good for mobile users



• Keyless data entry tries to eliminate high volume input errors, using optical character recognition (OCR) or bar codes

• Pen input is often used for simpler data• Graphical user interfaces are the de facto

standard for most applications• E-mail has grown into groupware, for

coordinating activities



• Electronic data interchange (EDI) conducts transactions among businesses

• Image and document interchange is like EDI; but captures literal images (photos)

• Middleware helps apps communicate with each other, such as ODBC database systems

• These options may be used company-wide, or left for individual projects to select


Process Architecture

• Software development environments (SDE’s) are generally selected to match the network architecture– How a system will be deployed affects how

it is developed

• Centralized and distributed presentation typically use COBOL, with a CICS transaction monitor, and VSAM or DB2 for managing files and data



• Two-tier client/server is the most mature option for selecting an SDE– Tools like PowerBuilder, Delphi, Visual Studio

are available; SQL commands are understood by all major database engines

– Testing, debugging, testing, writing, and help authoring tools are also available

– Clean layering enforces separate presentation, application, and data layers



• Multi-tier client/server typically must support 1000+ users and 1+ TB databases– Client and server must support cross-platform

environment - Windows, Unix, Mac– Coding is often object-oriented; C++, C#,

Ada95, Smalltalk, etc.– Tools include Forté, IBM VisualAge, etc.



• Network computing uses purely Internet-based tools– HTML for page content and hyperlinks– Computer Gateway Interface (CGI)

components, using Perl, Visual Basic’s ActiveX, etc.

– Java and its cousins– XML (= SGML lite) to enhance understanding

of document content


Application Architecture Strategy

• Enterprise AA strategy defines corporate standards for technology, tools, processes

• Tactical AA strategy defines standards from scratch for each project, based on their research and needs

• A key part of these choices is whether to buy existing tools, or build custom ones


Network Topology Overview

• There are four major topologies (structures) for a physical computer network– Bus– Ring– Star– Hierarchical

• Each may use specific protocols (languages) to communicate among the computers


Network Topology - Bus

• A key function to achieve connectivity among computers is definition of the network topology

• The “bus” is the simplest topology - it connects computers along a single line

• A peer-to-peer (serverless) network uses the bus topology, with AppleTalk or Ethernet


Ring Topology

• The ring topology connects computers in a loop, and passes packets of data from one computer to the next

• IBM’s Token Ring is the most famous example

• Bad if a computer falls off the network – hard to tell who dropped the packet


Star Network

• Many clients may be connected to each server across a star network

• The middle of each star is a server

• Servers are connected to each other

• Very common – think of using a server for each department, and be able to control which departments can see each other


Hierarchical Network

• This is a set of nested star networks, looks kind of like an organization chart

• Generally the servers get smaller the further down the hierarchy

• Sometimes used in very large corporations, where the biggest servers store company-wide or division-wide data


Network Protocols

• Networks allow computers to communicate using standard languages (protocols)– Most common are Ethernet and TCP/IP– Others include Token Ring, IPX, SNA,

and AppleTalk

• Network operating systems – Windows 2000 Server & 2003 Server, Unix,

Linux, NetWare, OS/2, Mac OS X Server

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