Software Engineering (v)

Demand analysis

Tasks for demand Analysis

Determine the overall requirements for the system
1. Functional Requirements
2. Performance requirements
such as: the corresponding time (speed), main memory capacity, disk capacity, security, and so on.
3. Reliability and Availability requirements
4. Error handling requirements
The action taken when the system discovers an error is mainly set in the critical part of the system.
5. Interface Requirements
User interface, hardware interface, software interface, communication interface, etc.
6. Constraints
Precision, tools and language, design constraints, hardware constraints, standards, and more.
7. Reverse Demand
8. possible future Requests

Data requirements for the analysis system
By establishing a data model to analyze, such as data dictionary, hierarchical block diagram, Warnier diagram, and the data structure normalization.

Export the logical model of a system
It includes complete data flow diagram, entity-Contact diagram, state transition diagram, database dictionary, main processing algorithm (IPO map), etc.
Fixed system development Plan
Revise the development schedule, etc.

Ways to communicate with users to obtain requirements
Interview
Formal interview: The system analyst presents a pre-prepared question.
Informal interview: Ask some open questions that users can freely answer and encourage respondents to say what they think.
When you need to access a large number of people, use a questionnaire to access it better.

Top-down refinement for data streams
With the help of data flow chart, database dictionary, IPO map and so on, refine and perfect detailed data flow chart, wait for each processing link corresponding function.

Simple Application Specification Technology
Team-oriented Requirements Collection method: (User and developer cooperation)
1) Preliminary interview;
2) Developers and users write "product requirements" separately;
3) A meeting to discuss, the respective display needs list;
4) arrive at a consensus to develop a small specification for the requirements list;
5) Draft the complete software requirements specification according to the results of the Conference.

Quickly build software prototypes
Quickly establish a program that demonstrates the main functions of the target system.
Common methods and tools:
(1) Fourth generation technology
(2) Reusable software components
(3) Formal specification and prototype environment

Analysis Modeling and Specification
Model: Just to understand an abstraction of things to things, is a kind of non-ambiguous written description of things.

Analytical modeling
In order to develop complex systems, the characteristics (data model, function model, behavior model) of the target system should be abstracted from different angles (models).
1) Entity Contact Diagram: Establish a data model to describe the relationship between data objects and data objects;
2) streaming diagram: The basis of building a functional model;
3) state transition diagram: Describes how the system transitions between state and state.

Entities-Contact diagram
Data Objects
Data objects can be external entities, things, behaviors, events, roles, units, locations, structures, and so on.

Property
Property defines the nature of the data object.

Contact
(1) One-on-one contact (1:1)
(2) One-to-many links (1:n)
(3) Many-to-many links (m:n)
In the ER diagram, the contact is represented by a diamond-shaped box.

Example diagram:

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Software Engineering (v)