1-1 Software Development Objectives: Discuss the goals of software development Identify various aspects of software quality Examine two development life cycle models Explore the notation of the Unified Modeling Language (UML) Examine issues related to error handling Introduce the concept of algorithm analysis

1-2 Software Development Software Engineering – make s/w development a rigorous engineering discipline; study of techniques and theory that support the development of high-quality software Focus on controlling the development process to achieve consistently good results We want to: – satisfy the client – the person or organization who sponsors the development – meet the needs of the users – the people using the software for its intended purpose

1-3 Goals of Software Engineering Solve the right problem – more difficult than it might seem – client interaction is key (social?) Deliver a solution on time and under budget – there are always trade-offs Deliver a high-quality solution – beauty is in the eye of the beholder – we must consider the needs of various stakeholders

1-4 FIGURE 1.1 Aspects of software quality

1-5 Development Models A development life cycle defines a process to be followed during product development Many software development models have been introduced All of them address the following fundamental issues in one way or another: – problem specification (gather requirements) – design – implementation – evaluation – testing and debugging – maintenance and evolution

1-6 Problem Specification We must specify the requirements of the software system Must be based on accurate information Various techniques: – discussions and negotiations with the client – modeling the problem structure and data flow – observation of client activities – analysis of existing solutions and systems

1-7 Design We must develop a solution You would not consider building a bridge without a design Design involves determining: – the overall software structure (architecture) – the key objects, classes, and their relationships Alternatives should be considered Mostly program language independent

1-8 Implementation We must turn the design into functional software Too many people consider this the primary act of software development May involve the reuse of existing software components

1-9 Evaluation/Analysis We must verify that the system conforms to the requirements This includes, but goes way beyond, testing code with test cases It is possible to build a system that has no bugs and yet is completely wrong Is system responsive enough?

1-10 Maintenance/Evolution After a system is initially developed, it must be maintained This includes: – fixing errors – making enhancements to meet the changing needs of users (evolution) The better the development effort, the easier the maintenance tasks will be

1-11 The Waterfall Model One of the earliest development models Each stage flows into the next Driven by documentation Advantages: – Lays out clear milestones and deliverables – Has high visibility – managers and clients can see the status Disadvantages: – late evaluation – not realistic in many situations

1-12 FIGURE 1.2 The waterfall software development model Specification

1-13 The Spiral Model Developed by Barry Boehm in the mid '80s Embraces an iterative process, where activities are performed over and over again for different aspects of the system Designed to reduce the risks involved Continually refines the system Each loop through the spiral is a complete phase of development

1-14 FIGURE 1.3 The spiral model of software development

1-15 The Unified Modeling Language The Unified Modeling Language (UML) has become a standard notation for software design It is unified in the sense that it is the synthesis of three separate notations It is language independent It includes various types of diagrams which use specific icons and notations However, it is flexible – the details you include in a given diagram depend on what you are trying to capture and communicate

1-16 UML Class Diagrams UML class diagrams may include: – The classes used in the system – The static relationships among classes – The attributes and operations of each class – The constraints on the connections among objects An attribute is class level data, including variables and constants An operation is essentially equivalent to a method May include visibility details

1-17 FIGURE 1.5 LibraryItem class diagram

1-18 FIGURE 1.6 A UML class diagram showing inheritance relationships

1-19 FIGURE 1.7 A UML class diagram showing an association

1-20 FIGURE 1.8 One class shown as an aggregate of other classes

1-21 Error Handling How problems are handled in a software system is a key design element In Java, an error generally represents an unrecoverable situation An exception is an unusual situation that might be handled in various ways Design questions include: – how are problems identified? – where are exceptions thrown and caught?

1-22 Analysis of Algorithms An aspect of software quality is the efficient use of resources, including the CPU Algorithm analysis is a core computing topic It gives us a basis to compare the efficiency of algorithms Example: which sorting algorithm is more efficient?

1-23 Growth Functions Analysis is defined in general terms, based on: – the problem size (ex: number of items to sort) – key operation (ex: comparison of two values) A growth function shows the relationship between the size of the problem (n) and the time it takes to solve the problem t(n) = 15n n

1-24 Growth Functions It's not usually necessary to know the exact growth function The key issue is the asymptotic complexity of the function – how it grows as n increases Determined by the dominant term in the growth function This is referred to as the order of the algorithm We often use Big-Oh notation to specify the order, such as O(n 2 )

1-25 FIGURE 1.11 Some growth functions and their asymptotic complexity

1-26 FIGURE 1.12 Increase in problem size with a ten-fold increase in processor speed

1-27 FIGURE 1.13 Comparison of typical growth functions

1-28 Analyzing Loop Execution A loop executes a certain number of times (say n) Thus the complexity of a loop is n times the complexity of the body of the loop When loops are nested, the body of the outer loop includes the complexity of the inner loop

1-29 Analyzing Loop Execution The following loop is O(n): for (int i = 0; i < n; ++i) { x = x + 1; }

1-30 Analyzing Loop Execution The following loop is O(n 2 ) because the loop executes n times, and the inner loop is O(n): for (int i = 0; i<n; ++i) { x = x + 1; for (int j = 0; j < n; ++j) { y = y - 1; }

1-31 SE and Data Structures The data structures examined we will examine lay the foundation for developing complex software Software Engineering techniques are needed as our software grows more complex As we discuss data structures, we will also practice good software engineering

1-32 Testing/Debugging w/assertions Use assert statement to assist debugging Can be turned off – don’t use to check preconditions Point p1 = new Point (); Point p2 = new Point (3, 4); double distance = p1.computeDistanceTo (p2); assert (Math.abs (distance – 5.0) < : "Distance incorrect");