October 30, 2019
Amitraj
System design is the phase that bridges the gap between problem domain and the existing system in a manageable way. This phase focuses on the solution domain, i.e. “how to implement?”
It is the phase where the SRS document is converted into a format that can be implemented and decides how the system will operate.
In this phase, the complex activity of system development is divided into several smaller sub-activities, which coordinate with each other to achieve the main objective of system development.
Inputs to System Design
System design takes the following inputs −
->Statement of work
->Requirement determination plan
->Current situation analysis
->Proposed system requirements including a conceptual data model, modified DFDs, and Metadata (data about data).
Outputs for System Design
System design gives the following outputs −
->Infrastructure and organizational changes for the proposed system.
->A data schema, often a relational schema.
->Metadata to define the tables/files and columns/data-items.
->A function hierarchy diagram or web page map that graphically describes the program structure.
->Actual or pseudocode for each module in the program.
->A prototype for the proposed system.
Types of System Design
Logical Design
Logical design pertains to an abstract representation of the data flow, inputs, and outputs of the system. It describes the inputs (sources), outputs (destinations), databases (data stores), procedures (data flows) all in a format that meets the user requirements.
While preparing the logical design of a system, the system analyst specifies the user needs at level of detail that virtually determines the information flow into and out of the system and the required data sources. Data flow diagram, E-R diagram modeling are used.
Physical Design
Physical design relates to the actual input and output processes of the system. It focuses on how data is entered into a system, verified, processed, and displayed as output.
It produces the working system by defining the design specification that specifies exactly what the candidate system does. It is concerned with user interface design, process design, and data design.
It consists of the following steps −
->Specifying the input/output media, designing the database, and specifying backup procedures.
->Planning system implementation.
->Devising a test and implementation plan, and specifying any new hardware and software.
->Updating costs, benefits, conversion dates, and system constraints.
Architectural Design
It is also known as high level design that focuses on the design of system architecture. It describes the structure and behavior of the system. It defines the structure and relationship between various modules of system development process.
Detailed Design
It follows Architectural design and focuses on development of each module.
Conceptual Data Modeling
It is representation of organizational data which includes all the major entities and relationship. System analysts develop a conceptual data model for the current system that supports the scope and requirement for the proposed system.
The main aim of conceptual data modeling is to capture as much meaning of data as possible. Most organization today use conceptual data modeling using E-R model which uses special notation to represent as much meaning about data as possible.
Entity Relationship Model
It is a technique used in database design that helps describe the relationship between various entities of an organization.
Terms used in E-R model
1.ENTITY − It specifies distinct real world items in an application. For example: vendor, item, student, course, teachers, etc.
2.RELATIONSHIP − They are the meaningful dependencies between entities. For example, vendor supplies items, teacher teaches courses, then supplies and course are relationship.
3.ATTRIBUTES − It specifies the properties of relationships. For example, vendor code, student name. Symbols used in E-R model and their respective meanings −
-> Entity
->Weak Entity
->Relationship
->Identity Relationship
->Attributes
->Key Attributes
->Multivalued
->Composite Attribute
->Derived Attribute
->Total Participation of E2 in R
->Cardinality Ratio 1:N for E1:E2 in R
Three types of relationships can exist between two sets of data: one-to-one, one-to-many, and many-to-many.
It is the phase where the SRS document is converted into a format that can be implemented and decides how the system will operate.
In this phase, the complex activity of system development is divided into several smaller sub-activities, which coordinate with each other to achieve the main objective of system development.
Inputs to System Design
System design takes the following inputs −
->Statement of work
->Requirement determination plan
->Current situation analysis
->Proposed system requirements including a conceptual data model, modified DFDs, and Metadata (data about data).
Outputs for System Design
System design gives the following outputs −
->Infrastructure and organizational changes for the proposed system.
->A data schema, often a relational schema.
->Metadata to define the tables/files and columns/data-items.
->A function hierarchy diagram or web page map that graphically describes the program structure.
->Actual or pseudocode for each module in the program.
->A prototype for the proposed system.
Types of System Design
Logical Design
Logical design pertains to an abstract representation of the data flow, inputs, and outputs of the system. It describes the inputs (sources), outputs (destinations), databases (data stores), procedures (data flows) all in a format that meets the user requirements.
While preparing the logical design of a system, the system analyst specifies the user needs at level of detail that virtually determines the information flow into and out of the system and the required data sources. Data flow diagram, E-R diagram modeling are used.
Physical Design
Physical design relates to the actual input and output processes of the system. It focuses on how data is entered into a system, verified, processed, and displayed as output.
It produces the working system by defining the design specification that specifies exactly what the candidate system does. It is concerned with user interface design, process design, and data design.
It consists of the following steps −
->Specifying the input/output media, designing the database, and specifying backup procedures.
->Planning system implementation.
->Devising a test and implementation plan, and specifying any new hardware and software.
->Updating costs, benefits, conversion dates, and system constraints.
Architectural Design
It is also known as high level design that focuses on the design of system architecture. It describes the structure and behavior of the system. It defines the structure and relationship between various modules of system development process.
Detailed Design
It follows Architectural design and focuses on development of each module.
Conceptual Data Modeling
It is representation of organizational data which includes all the major entities and relationship. System analysts develop a conceptual data model for the current system that supports the scope and requirement for the proposed system.
The main aim of conceptual data modeling is to capture as much meaning of data as possible. Most organization today use conceptual data modeling using E-R model which uses special notation to represent as much meaning about data as possible.
Entity Relationship Model
It is a technique used in database design that helps describe the relationship between various entities of an organization.
Terms used in E-R model
1.ENTITY − It specifies distinct real world items in an application. For example: vendor, item, student, course, teachers, etc.
2.RELATIONSHIP − They are the meaningful dependencies between entities. For example, vendor supplies items, teacher teaches courses, then supplies and course are relationship.
3.ATTRIBUTES − It specifies the properties of relationships. For example, vendor code, student name. Symbols used in E-R model and their respective meanings −
-> Entity
->Weak Entity
->Relationship
->Identity Relationship
->Attributes
->Key Attributes
->Multivalued
->Composite Attribute
->Derived Attribute
->Total Participation of E2 in R
->Cardinality Ratio 1:N for E1:E2 in R
Three types of relationships can exist between two sets of data: one-to-one, one-to-many, and many-to-many.
