Object Oriented Analysis is popular approach that sees a system from the viewpoint of the objects themselves as they function and interact

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1 Chapter 6 Object Oriented Analysis is popular approach that sees a system from the viewpoint of the objects themselves as they function and interact Object-oriented (O-O) analysis describes an information system by identifying things called objects. An object represents a real person, place, event, or transaction. Object-oriented analysis is a popular approach that sees a system from the viewpoint of the objects themselves as they function and interact with the system. Object Model - describes objects, which combine data and processes. Object models are the end product of object-oriented analysis. There are an array of terms and concepts use regarding Object-Oriented Analysis - Unified Modeling Language - UML is a widely used method of visualizing and documenting software systems design. - Attributes - A single characteristic or fact about an entity. An attribute, or field, is the smallest piece of data that has meaning within an information system. For example, a Social Security number or company name could be examples of an attribute. In object-oriented analysis, an attribute is part of a class diagram that describes the characteristics of objects in the class. Also known as a data element. - Methods - A method defines specific tasks that an object must perform. A method describes what and how an object does something. - Message - A message is an object-oriented command that tells an object to perform a certain method. - Class - A term used in object-oriented modeling to indicate a collection of similar objects. - Instance - A specific member of a class. Objects Consider how the UML describes a family with parents and children. The UML represents an object as a rectangle with the object name at top, followed by the objects attributes and methods. The CHILD object possesses the same attributes as the PARENT object and an additional attribute that shows the number of siblings. A CHILD object performs certain methods. The family also might have a DOG object. Attributes If objects are similar to nouns, attributes are similar to adjectives that describe the characteristics of an object. Some objects might have a few attributes; others might have dozens. Methods A method defines specific tasks that an object can perform. Just as objects are similar to nouns and attributes are similar to adjectives,

2 methods resemble verbs that describe what and how an object is doing something. Messages Polymorphism - The concept that a message gives different meanings to different objects (e.g., a GOOD NIGHT message might produce different results depending if it is received by a child or the family dog). Black Box - A metaphor for a process or action that produces results in a nontransparent or non-observable manner. In data flow diagrams, a process appears as a black box where the inputs, outputs, and general function of the process are known, but the underlying details are not shown. Encapsulation - The idea that all data and methods are self-contained, as in a black box. A major advantage of O-O designs is that systems analysts can save time and avoid errors by using modular objects, and programmers can translate the designs into code, working with reusable program modules that have been tested and verified. Classes An object belongs to a group or category called a class. Relationships - Describe what objects need to know about each other, how objects respond to changes in other objects, and the effects of membership in classes, superclasses, and subclasses Object Relationship Diagram After you identify objects, classes, and relationships, you are ready to prepare an object relationship diagram that will provide an overview of the system. You will use that model as a guide as you continue to develop additional diagrams and documentation. Object Modelling with the UML The UML uses a set of symbols to represent graphically the various components and relationships within a system. It mainly is used to support object-oriented system analysis to develop object models. State Transition Diagrams Shows how an object changes from one state to another, depending on events that affect the object. In a state transition diagram, the states appear as rounded rectangles with the state names inside. The small circle to the left is the initial state, or the point where the object first interacts with the system Reading from left to right, the lines show direction and describe the action or event that causes a transition from one state to another The circle at the right with a hollow border is the final state Activity Diagrams Shows the order in which the actions take place and identify the outcomes. They also can display multiple use cases in the form of

3 a grid, where classes are shown as vertical bars and actions appear as horizontal arrows. CASE Tools - Object modeling requires many types of diagrams to represent the proposed system Creating the diagrams by hand is time- consuming and tedious, so systems analysts rely on CASE tools to speed up the process and provide an overall framework for documenting the system components! You should develop an object relationship diagram that provides an overview of the system! You should organize your use cases and use case diagrams so they can be linked to the appropriate class, state transition, sequence, and activity diagrams! It is much easier to repair a diagram now than to change the software later Chapter 7 SYSTEM ARCHITECTURE Architecture Checklist Enterprise Resource Planning (ERP)! Objective to establish company-wide strategy for using IT resources.! It defines specific architecture, including standards for data, processing, network and UI design.! Advantage: describes a specific hardware and software environment called a platform that ensures connectivity and easy integration of future systems, including in-house software and commercial packages.! A single computer system can support various departments across organisation.! Supply Chain Management (SCM) many companies are extending ERP systems to their suppliers and customers. Initial Cost and TCO Consider choices made (e.g. in-house development or outsourcing), new types of outsourcing. Have there been any economic, government, or regulatory events that could affect project? Consider technological advancements, changes in major assumptions in make or buy decision, any merger/acquisition issues, any new trends in the marketplace, and has the original TCO estimate been updated? All these things could affect initial cost and TCO. Scalability! Also called extensibility.! Refers to system s ability to expand, change or downsize easily to meet changing needs of the enterprise.! Important in implementing volume-based systems such as transaction processing systems (TPS). Web Integration

4 ! Will a new application be part of an e-commerce strategy and will it integrate with other Web-based components. Legacy System Interface Requirements! New system may need to interact with legacy systems older systems run on mainframe computers.! Systems analyst must determine how the new application will communicate with existing legacy systems.! This involves analysis of data formats and compatibility.! Legacy file data may need to be converted expensive and timeconsuming.! Will the new application eventually replace legacy system? Processing Options How will the system process data online (24/7) or in batches?! High-capacity TPS, such as order entry system, requires more network, processing and data storage resources compared to monthly billing system that handles data in batches.! If system must operate online, provision must be made for backup and speedy recovery in the event of system failure Security Issues Planning Servers Server computer that supplies data, processing services and other support to one or more computers, called clients. Mainframe architecture where the server performs ALL processing. " Mainframe architecture used to be the only system design available. " Early systems performed all data input/output at one central location data processing centre. Users had no input/output capability, except for printed reports distributed by IT department. Server-based Processing Terminal - a keyboard and display screen to handle input/output from remote locations but lacked independent processing capability. Clients Stand-alone Computing - workstation performs ALL the functions of a server by storing, accessing, and processing data as well as providing UI. Local Area Network (LAN) allows sharing of data and hardware/resources. One or more LANs can connect to a centralised server. Wide Area Network (WAN) spans long distances and can connect LANs that are continents apart. Distributed System company-wide systems that connect one or more LANs or WANs these systems increase concerns about data security and integrity. Client-based Processing File Server Design " An individual LAN client has a copy of the application program installed locally, while data is stored on central file server. The client requests a copy of data file and server transmits entire data file to client.

5 Middleware N-tier system middle layer uses special software called middleware enables tiers to communicate and pass data back and forth. Glue that holds clients and servers together. Software that mediates between an application and a network. Distributed Database Management System (DDBMS) Data can be in more than one location. Advantages! Data stored closer to users can reduce network traffic.! System is scalable new data sites can be added without reworking the design system.! System less likely to experience a catastrophic failure when data stored in various locations. Disadvantages! Data security harder to maintain controls and standards when data is stored in various locations.! Architecture of DDBMS is more complex and harder to manage. Internet-based Architecture Internet has had a huge impact on system architecture more than just a communication channel seen as a different environment for systems development. Developing E-Commerce Solutions In-House (Developing own website) Guidelines for In-House E-Commerce Site Development 1. Analyse the company s business needs and develop a clear statement of your goals. Consider the experience of other companies with similar projects. 2. Obtain input from users who understand the business and technology issues involved with the project. Plan for future growth, but aim for ease of use. 3. Determine whether the IT staff has the necessary skills and experience to implement the project. Consider training, additional resources, and the use of consultants if necessary. 4. Consider integration requirements for existing legacy systems or ERP. Select a physical infrastructure carefully, so it will support the application, now and later. 5. Develop the project in modular form so users can test and approve the functional elements as you go along. 6. Connect the application to the existing in-house systems and verify interactivity. 7. Test every aspect of the site exhaustively. Consider a preliminary rollout to a pilot group to obtain feedback before a full launch.