SA Capstone Requirements and Design Week 6 SYST Winter 2014

SA Capstone Requirements and Design Week 6 SYST36367 - Winter 2014
Some slides adapted from: Systems Analysis and Design in a Changing World, 6th Edition, Satzinger, Jackson, Burd, CENGAGE Learning, 2012

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

Analysis Objectives versus Design Objectives
Understand WHAT is required Design HOW to meet requirements Systems Analysis and Design in a Changing World, 6th Edition

Analysis vs. Design Models
The outputs of the Analysis phase become the input for the design phase Systems Analysis and Design in a Changing World, 6th Edition

UML Requirements vs. Design Models Diagrams are enhanced and extended
Systems Analysis and Design in a Changing World, 6th Edition

Systems Analysis and Design in a Changing World, 6th Edition
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 Goal is to build well structured and MAINTAINABLE code Get away from spaghetti code Systems Analysis and Design in a Changing World, 6th Edition

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 Models are extensions of requirements models Creating additional, more detailed models of the system Systems Analysis and Design in a Changing World, 6th Edition

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

Identifying System Interfaces Inputs/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. Can still be flat files (i.e. xml, JSON data structures) Systems Analysis and Design in a Changing World, 6th Edition

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 JSON is gaining in popularity due to its more compact nature Systems Analysis and Design in a Changing World, 6th Edition

Defining System Inputs Details Sequence Diagram Details for messages Systems Analysis and Design in a Changing World, 6th Edition

Design the Environment The 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 Systems Analysis and Design in a Changing World, 6th Edition

Network Diagram Internal 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 store Systems Analysis and Design in a Changing World, 6th Edition

Abstract Three Layer Architecture
These can be logical or physical Systems Analysis and Design in a Changing World, 6th Edition

Internal Deployment with Three Layer Architecture
Typically in web apps, view layer is generated on the app server and served to clients as html Systems Analysis and Design in a Changing World, 6th Edition

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

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

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

Performance improved by multiple server configurations Systems Analysis and Design in a Changing World, 6th Edition

Hosting Alternatives for Internet Deployment
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 Consider making sure your hosting is done on Canadian servers to ensure your data is subject to Canadian laws Systems Analysis and Design in a Changing World, 6th Edition

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) Very secure Systems Analysis and Design in a Changing World, 6th Edition

Virtual Private Network (VPN)

RMO’s Current Technology Architecture

Object-Oriented Program Flow Three Layer Architecture
Logical three-tiered architecture vs. physical three-tiered architecture Each object or system component has data as well program logic embedded in it Systems Analysis and Design in a Changing World, 6th Edition

Fundamental Design Principles
Encapsulation Restricting access to the object’s inner workings User of your class should not know or care how your class is implemented Each class should hold the responsibility for ensuring proper maintenance of its current internal state Only declaring attributes and methods as public when necessary It is best to have classes that are well encapsulated Example of having to call method A before calling method B. Also leads to a tightly coupled relationship

Coupling A quantitative measure of how closely related classes are linked (tightly or loosely coupled) Two classes are tightly coupled if 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 A high level of coupling results in a high level of co-dependency between classes. Any changes made to a class must be done very carefully with dependency in mind. Example of a method call with many params vs. a method call with one “message” parameter Systems Analysis and Design in a Changing World, 6th Edition

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 class 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 Do one thing and do it well! Example of customer class also maintaining vendor information Class that accesses internet and database Systems Analysis and Design in a Changing World, 6th Edition

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 Three-tiered architecture plus decoupled handles this relatively well Don’t have login information sprinkled throughout the app! Systems Analysis and Design in a Changing World, 6th Edition

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 MVC is considered a good use of indirection Systems Analysis and Design in a Changing World, 6th Edition

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. CRC  Class Responsibility Collaboration Systems Analysis and Design in a Changing World, 6th Edition

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, Yii, jQuery, Bootstrap, 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 Systems Analysis and Design in a Changing World, 6th Edition

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

Controller Pattern First step toward multilayer architecture More design patterns are at the end of the chapter Reduce coupling between view layer and problem domain/business layer classes Acts as a intermediary between outside world and internal system Acts as a switchboard Systems Analysis and Design in a Changing World, 6th Edition

OO Detailed Design Steps Chapters 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 Systems Analysis and Design in a Changing World, 6th Edition

Start with Domain Class Diagram RMO Sales Subsystem
Further elaborate the attributes Systems Analysis and Design in a Changing World, 6th Edition

Create First Cut Design Class Diagram Use Case Create phone sale with controller added Denotes Navigation Visibility Navigability often modelled as attributes (example Customer could have a collection each representing a Sale) Controller classes are utility classes that help in the processing of a use case Systems Analysis and Design in a Changing World, 6th Edition

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

Start with System Sequence Diagram (SSD) Use case Create customer account Return messages in this case are simply for customer to verify… Systems Analysis and Design in a Changing World, 6th Edition

Sequence Diagram to show View Layer and Part of Problem Domain Layer
Messages are method calls data passed in is the parameters Systems Analysis and Design in a Changing World, 6th Edition

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

Create Customer Account Use Case Start with domain model for Customer Account Subsystem Systems Analysis and Design in a Changing World, 6th Edition

Create Customer Account Use Case First cut design class diagram for use case Select needed classes, elaborate attributes, add controller, and add navigation visibility Honing down on the attributes Systems Analysis and Design in a Changing World, 6th Edition

Create Customer Account Use Case First cut sequence diagram expanding SSD, adding controller, and adding needed classes Note that Customer must have navigability to Address and Account Systems Analysis and Design in a Changing World, 6th Edition

Create Customer Account Use Case 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 Use case realization Get a good idea of the methods (and params) that have to be exposed Customer object takes on responsibility for Saving itself to the database creating Address and Account classes directly  customer “owns” these classes (composition) Systems Analysis and Design in a Changing World, 6th Edition

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

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

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

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:

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

SA Capstone Requirements and Design Week 6 SYST Winter 2014

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