Chapter 1 : Object Oriented Analysis and Design

Chapter 1 : Object Oriented Analysis and Design

Chapter 1 Object-Oriented Analysis and Design Disclaimer Slides come from a variety of sources: Craig Larman-developed slides; author of this classic textbook. Dr. Constantinos Constantinides, University of London Slides from the University of Pittsburg Slides from many of my existing slides on these same topics New slides from sources unknown

2 Chapter 1 Chapter one covers a host of many topics central to todays technologies. These skills are essential in todays professional community. We will talk about (in some detail) iterative development, evolutionary development, the Unified Process, agile approaches, UML, Later on we will advance into more complex concepts that address framework design and architectural analysis. Please note that the materials are meant to be foundational. 3

Thinking in Objects and UML - 1 The Unified Modeling Language (UML) is a standard diagramming notation; sometimes referred to as a blueprint. It is NOT OOA/OOD or a method Only a notation for capturing objects and the relationships among objects (dependency; inheritance; realizes; aggregates, . .) UML is language-independent Analysis and design provide software blueprints captured in UML. Blueprints serve as a tool for thought and as a form of communication with others. 4 Thinking in Objects and UML 2 But it is far more essential to think in terms of objects as providing services and accommodating responsibilities. Discuss: What is meant by services? How indicated?

How might you think these services impact the design of classes? How might a client access these services? What is encapsulation? How does it relate to reusability? Selfgovernance? Design? Discuss: What is meant by responsibilities? Encapsulation of data and services? 5 Thinking in Terms of Objects and UML - 3 Object-Oriented Analysis (Overview) An investigation of the problem (rather than how a solution is defined) During OO analysis, there is an emphasis on finding and describing the objects (or concepts) in the problem domain. For example, concepts in a Library Information System include Book, and Library.

High level views found in the application domain. Oftentimes called domain objects; entities. 6 Thinking in Terms of Objects and UML - 4 Object-Oriented Design Emphasizes a conceptual solution that fulfills the requirements. Need to define software objects and how they collaborate to meet the requirements. For example, in the Library Information System, a Book software object may have a title attribute and a getChapter method. What are the methods needed to process the attributes? Designs are implemented in a programming language. In the example, we will have a Book class in Java.

7 Thinking in Terms of Objects and UML 5 From Design to Implementation Analysis investigation of the problem Book (concept) Domain concept Design logical solution

Book title print() Representation in analysis of concepts Construction code public class Book { public void print(); private String title; } Representation in an object-oriented

programming language. Can you see the services / responsibilities in the Book class? 8 Thinking in Objects and UML-6 Then too, there are sets of proven design solutions to problems that are considered best practices. Certain groupings of classes with specific responsibilities / interfaces. These provide specific solutions to specific problems. Called Design Patterns We will discuss (much later) these standard patterns and how to apply them to develop solutions to common design problems.

9 Thinking in Objects and UML-7 Of course, design (solution to requirements) assume a robust requirements analysis has taken place. Use Cases are often used to capture stories of requirements and are often views as constituting the functional requirements, but NOT the software quality factors (non-functional requirements). Use Cases are not specifically designed to be object-oriented, but rather are meant to capture how an application will be used. Many methods for capturing requirements. We will concentrate on Use Cases (ahead). 10 Basic Terms: Iterative, Evolutionary, and Agile

1. Introduction Iterative - the entire project will be composed of min-projects and will iterate the same activities again and again (but on different part of the project AND with different emphases) until completion. Evolutionary (or incremental) - the software grows by increments (to be opposed to the traditional, and somewhat oldfashioned, Waterfall model of software development). Agile - we will use a light approach to software development

rather than a very rigid one (which may be needed for a safetycritical system for example) This kind of approach seems better at treating software development as a problem solving activity; also the use of objects makes it amenable. 11 Our Approach: We need a Requirements Analysis approach with OOA/OOD need to be practiced in a framework of a development process. We will adopt an agile approach (light weight, flexible) in the context of the Unified Process, which can be used as a sample iterative development process. Within this process, the principles can be discussed. Please note that there are several other contexts that may be used, such as Scrum, XP, Feature-Driven Development, Lean

Development, Crystal Methods and othersand we will look at a few of these. 12 Why the Unified Process: The Unified Process is a popular iterative software development process. Iterative and evolutionary development involves relatively early programming and testing of a partial system, in repeated cycles. It typically also means that development starts before the exact software requirements have been specified in detail; Feedback (based on measurement) is used to clarify, correct and improve the evolving specification: This is in complete contrast to what we usually mean by engineering! 13

2. What is the Unified Process? The UP is very flexible and open and can include other practices from other methods such as Extreme Programming (XP) or Scrum for example. e.g. XPs test-driven development, refactoring can fit within a UP project; So can Scrums daily meeting. Being pragmatic in adapting a particular process to your needs is an important skill : all projects are different. 14 We will be studying all of the topics found in Fig. 1.1 OOA/D Patterns

UML notation Topics and Skills Principles and guidelines Requirements analysis Iterative development with an agile Unified Process The Rush to Code

Critical ability to develop is to think in terms of objects and to artfully assign responsibilities to software objects. Talk at great length in COP 3538 about encapsulation and assigning methods to objects where the data is defined One cannot design a solution if the requirements are not understood. One cannot implement the design if the design is faulty. If I could only stop my students. 16 The Rush to Code Analysis: - investigate the problem and the requirements.

What is needed? Required functions? Investigate domain objects. Problem Domain The Whats of a system. Do the right thing (analysis) Design: Conceptual solution that meets requirements.

Not an implementation E.g. Describe a database schema and software objects. Avoid the CRUD activities and commonly understood functionality. The Solution Domain The Hows of the system Do the thing right (design) 17 What is Object-Oriented Analysis and Design OOA: we find and describe business objects or concepts in the problem domain OOD: we define how these software objects collaborate to meet the requirements. Attributes and methods. OOP: Implementation: we implement the design objects in,

say, Java, C++, C#, etc. 18 Homework Assignment #1 due: 19 Sep start of class. Hardcopy please. Using the model below, develop a two-three page discussion Define Use Cases Define Domain Model Define Interaction Diagrams Define Design Class Diagrams

outlining the four activities listed and present the major features of each. A short definition and example of a domain model, interaction diagram, and class diagram is sufficient, but be prepared to discuss each of these. Also, have a general idea about use cases what they are designed to do and what they are not designed to do. 19 Homework Assignment #1 (continued) Be aware that this concludes chapter 1. But there are a number of pages in this chapter that I have not explicitly discussed in class. You are responsible for these, and some of this may appear in your midterm exams.

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