some slides adapted from:

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SA Capstone Requirements and Design

Week 6

SYST36367 - Winter 2013Instructors: Jerry Kotuba & Joe Varrasso

Some slides adapted from: Systems Analysis and Design in a Changing World, 6th Edition, Satzinger, Jackson, Burd, CENGAGE Learning, 2012

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Lesson Objectives

Analysis versus Design Designing the software architecture Design Principles Selecting software frameworks and components Design Patterns Design Class Diagrams Sequence Diagrams

Systems Analysis and Design in a Changing World, 6th Edition 3

Analysis Objectives versus Design Objectives

Understand WHAT is required

Design HOW to meet requirements


Analysis vs. Design Models


UML Requirements vs. Design Models

Diagrams are enhanced and extended


Two Levels of Design

Architectural Design Broad design of the overall system structure Also called General Design and Conceptual Design

Detailed Design Low level design that includes the design of the specific

program details Design of each use case Design of the database Design of user and system interfaces Design of controls and security


Design Activities:Design the application architecture and software

Partition system into subsystems Define software architecture

Two layer, three layer or model-view-controller Detailed design of each use case

Design class diagrams Sequence diagrams State machine diagrams


Design Activities:Design the system interfaces

Information systems interact with many other systems, internal and external Much more integration now

System interfaces connect with other systems in many different ways Save data another system uses Read data another system saved Real time request for information Software services


Identifying System InterfacesInputs/outputs with minimal human intervention

Inputs from and outputs to other systems These are direct interfaces with other information

systems, normally formatted as network messages. Highly automated inputs and outputs

These are captured by devices (such as scanners) or generated by persons who start a process that proceeds without further human intervention.

Inputs and outputs to external databases These can supply input to or accept output from a

system.


Identifying System Interfaces


XML for System Interfaces Extensible Markup Language (XML) -- extension of HTML that

embeds self-defining data structures within textual messages XML tags -- character sequences (such as <name> and </name>) that define

the beginning, end, and meaning of the text that appears between them


Defining System Inputs Details Sequence

Diagram Details for

messages


Design the EnvironmentThe design activity now in more detail

Design for Internal Deployment Stand alone software systems

Run on one device without networking Internal network-based systems

Local area network, client-server architecture Desktop applications and browser-based

applications Three-layer client server architecture

View layer, domain layer, and data layer Desktop and browser based applications


Network DiagramInternal Network System


Three Layer Architecture

Three Layer Client-Server Architecture a client/server architecture that divides an application into view

layer, business logic layer, and data layer

View layer the part of the three-layer architecture that contains the user

interface

Business logic layer or domain layer the part of a three-layer architecture that contains the

programs that implement the business rules and processes

Data layer the part of a three-layer architecture that interacts with the data


Abstract Three Layer Architecture


Internal Deployment withThree Layer Architecture


Design the Environment(continued)

Design for External Deployment Configuration for Internet deployment

Advantages and risks Hosting Alternatives for Internet deployment

Colocation Managed services Virtual Servers Cloud computing

Diversity of Client Devices with Internet deployment Full size, tablets and notebooks, smart phones


Configuration for Internet Deployment


Configuration for Internet Deployment Advantages

Accessibility—Web-based applications are accessible to a large number of potential users (including customers, suppliers, and off-site employees).

Low-cost communication—The high-capacity networks that form the Internet backbone were initially funded primarily by governments. Traffic on the backbone networks travels free of extra charges to the end user. Connections to the Internet can be purchased from a variety of private Internet service providers at relatively low costs.

Widely implemented standards—Web standards are well known, and many computing professionals are already trained in their use.


Configuration for Internet Deployment Potential Problems

Security—Web servers are a well-defined target for security breaches because Web standards are open and widely known. Wide-scale interconnection of networks and the use of Internet and Web standards make servers accessible to a global pool of hackers.

Throughput—When high loads occur, throughput and response time can suffer significantly. The configuration must support not only daily average users but also a peak-load number of users.

Changing standards—Web standards change rapidly. Client software is updated every few months. Developers of widely used applications are faced with a dilemma: Use the latest standards to increase functionality or use older standards to ensure greater compatibility with older user software.


Performance improved by multiple server configurations


Hosting Alternatives for Internet Deployment Hosting:

Running and maintaining a computer system on someone’s behalf where the application software and the database reside

The process of providing physical servers at a secure location and selling those services to other businesses that wish to deploy Web sites

Issues when considering hosting alternatives Reliability, security, physical facilities, staff, potential

for growth and cost


Hosting Alternatives for Internet Deployment (continued)


Design for Remote, Distributed Environment

Two interfaces to same Web app for internal vs. external access Back end, Front end UI to same Web app Not as secure

Virtual private network (VPN) Closed network with security and closed access built

on top of a public network (Internet)


Virtual Private Network (VPN)


RMO’s Current Technology Architecture


Object-Oriented Program FlowThree Layer Architecture


Fundamental Design Principles Coupling

A quantitative measure of how closely related classes are linked (tightly or loosely coupled)

Two classes are tightly coupled of there are lots of associations with another class

Two classes are tightly coupled if there are lots of messages to another class

It is best to have classes that are loosely coupled If deciding between two alternative designs, choose

the one where overall coupling is less


Fundamental Design Principles Cohesion

A quantitative measure of the focus or unity of purpose within a single class (high or low cohesiveness

One class has high cohesiveness if all of its responsibilities are consistent and make sense for purpose of the class (a customer carries out responsibilities that naturally apply to customers)

One class has low cohesiveness if its responsibilities are broad or makeshift

It is best to have classes that are highly cohesive If deciding between two alternative designs, choose

the one where overall cohesiveness is high


Fundamental Design Principles Protection from Variations

A design principle that states parts of a system unlikely to change are separated (protected) from those that will surely change

Separate user interface forms and pages that are likely to change from application logic

Put database connection and SQL logic that is likely to change in a separate classes from application logic

Use adaptor classes that are likely to change when interfacing with other systems

If deciding between two alternative designs, choose the one where there is protection from variations


Fundamental Design Principles Indirection

A design principle that states an intermediate class is placed between two classes to decouple them but still link them

A controller class between UI classes and problem domain classes is an example

Supports low coupling Indirection is used to support security by directing

messages to an intermediate class as in a firewall If deciding between two alternative designs, choose

the one where indirection reduces coupling or provides greater security


Fundamental Design Principles Object Responsibility

A design principle that states objects are responsible for carrying out system processing

A fundamental assumption of OO design and programming Responsibilities include “knowing” and “doing” Objects know about other objects (associations) and they

know about their attribute values. Objects know how to carry out methods, do what they are asked to do.

Note that CRC cards and the design in the next chapter involve assigning responsibilities to classes to carry out a use case.

If deciding between two alternative designs, choose the one where objects are assigned responsibilities to collaborate to complete tasks (don’t think procedurally).

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Software Components and Frameworks Time to Market is paramount in today’s competitive marketplace Selecting powerful and tested frameworks and components can

save lots of development time Systems Analysts often need to participate in “Buy versus Build”

decisions regarding components and frameworks Capstone is designed to reflect industry best practices. So your

team should look for components and frameworks that can speed your development and improve your product!

Past groups have used several components and frameworks including:– CakePHP, jQuery, Kendo UI, HTML5, PhoneGap, Google Web Toolkit

(GWT), Microsoft Entity Framework, ASP.NET MVC, ASP.NET AJAX Control Toolkit, Crystal Reports, etc.


Design Patterns

Design Pattern—standard design techniques and templates that are widely recognized as good practice

For common design/coding problems, the design pattern suggests the best way to handle the problem.

They are written up in design pattern catalogs/references. Include: Pattern name Problem that requires solution The pattern that solves the problem An example of the pattern Benefits and consequences of the a pattern


Design Patterns Design patterns became widely accepted after the

publication of Elements of Reusable Object-Oriented Software,(1996) by Gamma et al (the “Gang of Four”)

There are architectural design patterns talked about already Three layer or model-view-controller architecture

The first example of a programming design pattern shown is the Controller Pattern. Problem is deciding how to handle all of the messages from

the view layer to classes in the problem domain layer to reduce coupling

Solution is to assign one class between the view layer and the problem domain layer that receives all messages and acts as a switchboard directing messages to the problem domain


Controller Pattern

First step toward multilayer architecture

More design patterns are at the end of the chapter


OO Detailed Design StepsChapters 10 and 11


First Cut Design Class Diagram Proceed use case by use case, adding to the diagram Pick the domain classes that are involved in the use

case (see preconditions and post conditions for ideas) Add a controller class to be in charge of the use case Determine the initial navigation visibility requirements

using the guidelines and add to diagram Elaborate the attributes of each class with visibility and

type Note that often the associations and multiplicity are

removed from the design class diagram as in text to emphasize navigation, but they are often left on


Start with Domain ClassDiagram

RMO Sales Subsystem


Create First Cut Design ClassDiagram

Use Case Create phone sale with controller added


Use Case Realization with Sequence Diagrams Use case realization—the process of elaborating the

detailed design of a use case with interaction diagrams Two types of interaction diagrams

UML sequence diagram (emphasized in text) UML communication diagram (also introduced)

Sequence diagrams, aka use case realization sequence diagrams, extend the system sequence diagram (SSD) to show: View layer objects Domain layer objects (usually done first) Data access layer objects


Start with System Sequence Diagram (SSD)

Use case Create customer account


Sequence Diagram to show View Layer and Part of Problem Domain Layer


Notes of Expanded Sequence Diagram This is a two layer architecture, as the domain class

Customer knows about the database and executes SQL statements for data access

Three layer design would add a data access class to handle the database resulting in higher cohesiveness and loose coupling

Note :CustomerForm is an object of the CustomerForm class, :CustomerHandler is an object of the CustomerHandler class playing the role of a controller stereotype (both underlined becuase they are objects)

aC:Customer is an object of the Customer class known by reference variable named aC

Note: the create message to aC:Customer points to the object symbol to indicate create


Create Customer Account Use Case

Start with domain model for Customer Account Subsystem



First cut design class diagram for use case

Select needed classes, elaborate attributes, add controller, and add navigation visibility



First cut sequence diagram expanding SSD, adding controller, and adding needed classes



Add messages and activation to complete collaboration

This is just the domain layer

These domain classes handle data access, so this is a two layer architecture


Assumptions Perfect technology assumption—First encountered for use

cases. We don’t include messages such as the user having to log on.

Perfect memory assumption—We have assumed that the necessary objects were in memory and available for the use case. In multilayer design to follow, we do include the steps necessary to create objects in memory.

Perfect solution assumption—The first-cut sequence diagram assumes no exception conditions.

Separation of responsibilities—Design principle that recommends segregating classes into separate components based on the primary focus, such as user interface, domain, and data access


Implementation Issues Three Layer Design

View Layer Class Responsibilities Display electronic forms and reports. Capture such input events as clicks, rollovers,

and key entries. Display data fields. Accept input data. Edit and validate input data. Forward input data to the domain layer classes. Start and shut down the system.


Implementation Issues Three Layer Design Domain Layer Class Responsibilities

Create problem domain (persistent) classes. Process all business rules with appropriate logic. Prepare persistent classes for storage to the database.

Data Access Layer Class Responsibilities Establish and maintain connections to the database. Contain all SQL statements. Process result sets (the results of SQL executions) into

appropriate domain objects. Disconnect gracefully from the database.

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Deliverable 3 (Project Design) Let’s review Deliverable 3 together which is due in Week 9 For detailed instructions and a link to the rubric please visit:

http://sacapstone.wikidot.com/deliverable3instructions

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Group Meetings Please break into your Capstone Groups to plan and

work on Deliverable 3! We will be meeting with each group today to assess

your progress and provide some advice

some slides adapted from:

Documents

design objectives

design models systems

general design

controllerdetailed design

changing world

design models diagrams

extended systems analysis

securitysystems analysis