UNIT-II Software Requirement Analysis And Specification:
Need for SRS, Problem Analysis, Requirements Specification.
Software Design: Design objectives and principles. Module level concepts, Coupling and Cohesion. Design Notations and specifications. Structured Design Methodology, Object Oriented Design. Detailed Design: Detailed Design, Verification (Design Walkthroughs, Critical Design Review, Consistency Checkers), Metrics.
Design Notations
Design notations are largely meant to be used during the process of design and are used to represent design or design decisions. For a function oriented design, the design can be represented graphically or mathematically by the following:
✓ Data flow diagrams
✓ Data Dictionaries
✓ Structure Charts
✓ Pseudocode
Data Dictionaries
✓ A data dictionary is a file or a set of files that includes a database's metadata.
✓ The data dictionary hold records about other objects in the database, such as data ownership, data relationships to other objects, and other data.
✓ Typically, only database administrators interact with the data dictionary.
The data dictionary, in general, includes information about the following:
✓ Name of the data item
✓ Aliases
✓ Description/purpose
✓ Related data items
✓ Range of values
✓ Data structure definition/Forms
1. The name of the data item is self-explanatory.
2. Aliases include other names by which this data item is called DEO for Data Entry Operator and DR for Deputy Registrar.
3. Description/purpose is a textual description of what the data item is used for or why it exists.
4. Related data items capture relationships between data items e.g., total_marks must always equal to internal_marks plus external_marks.
5. Range of values records all possible values, e.g. total marks must be positive and between 0 to 100.
6. Data structure Forms: Data flows capture the name of processes that generate or receive the data items.
The scheme of organizing related information is known as ‘data structure’.
The types of data structure are:
Lists: A group of similar items with connectivity to the previous or/and next data items.
Arrays: A set of homogeneous values
Records: A set of fields, where each field consists of data belongs to one
data type.
Trees: A data structure where the data is organized in a hierarchical structure. This type of data structure follows the sorted order of insertion,
deletion and modification of data items.
Tables: Data is persisted in the form of rows and columns. These are similar to records, where the result or manipulation of data is reflected for the whole table.
✓ A structure chart (SC) in software engineering and
organizational theory is a chart which shows the breakdown of a system to its lowest manageable levels.
✓ They are used in structured programming to arrange program modules into a tree.
✓ Each module is represented by a box, which contains the module's name.
✓ Structure Chart partitions the system into black boxes (functionality of the system is known to the users but inner details are unknown).
✓ Structure Chart represent hierarchical structure of modules.
✓ Inputs are given to the black boxes and appropriate outputs are generated.
✓ Modules at top level called modules at low level.
✓ Components are read from top to bottom and left to right.
Symbols used in construction of structured chart 1.Module
It represents the process or task of the system. It is of three types.
1.Control Module: A control module branches to more than one sub module.
2.Sub Module: Sub Module is a module which is the part (Child) of another module.
3.Library Module: Library Module are reusable and invokable from any module.
2. Conditional Call: It represents that control module can select any of the sub module on the basis of some condition.
3. Loop (Repetitive call of module): It represents the repetitive execution of module by the sub module.
A curved arrow represents loop in the module. All the sub modules cover by the loop repeat execution of module.
4. Data Flow: It represents the flow of data between the modules. It is represented by directed arrow with empty circle at the end.
6. Physical Storage: Physical Storage is that where all the information are to be stored.
5. Control Flow: It represents the flow of control between the modules. It is represented by directed arrow with filled circle at the end.
Example : Structure chart for an Email server
✓ Pseudo code is a term which is often used in programming and algorithm based fields.
✓ It is a methodology that allows the programmer to represent the implementation of an algorithm.
✓ Pseudocode is a "text-based" detail (algorithmic) design tool.
Pseudocode
✓ Pseudo code: It’s simply an implementation of an algorithm in the form of notations and informative text written in plain English.
✓ It has no syntax like any of the programming language and thus can’t be compiled or interpreted by the computer.
✓ Pseudocode often uses structural conventions of a normal programming language, but is intended for human reading rather than machine reading.
How to write a Pseudo-code?
1.Arrange the sequence of tasks and write the pseudocode accordingly.
2.Start with the statement of a pseudo code which establishes the main goal or the aim.
Example:
This program will allow the user to check the number whether it's even or odd.
3. The way the if-else, for, while loops are indented in a program, indent the statements likewise, as it helps to comprehend the decision control and execution mechanism. They also improve the readability to a great extent. Example:
if "1“
print response
"I am case 1“
if "2"
print response
"I am case 2"
4. Use appropriate naming conventions. the naming must be simple and distinct.
5. Elaborate everything which is going to happen in the actual code. Don’t make the pseudo code abstract.
6. Use standard programming structures such as ‘if- then’, ‘for’, ‘while’, ‘cases’ the way we use it in programming.
7. Check whether all the sections of a pseudo code is complete, finite and clear to understand and comprehend.
Advantages of Pseudocode
✓ Improves the readability of any approach. It’s one of the best approaches to start implementation of an algorithm.
✓ Acts as a bridge between the program and the algorithm or flowchart. It works as a rough documentation, so the program of one developer can be understood easily when a pseudo code is written out.
✓ The main goal of a pseudo code is to explain what exactly each line of a program should do, hence making the code construction phase easier for the programmer.
