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System Design Cheat Sheet by

Essentials of Design and the Design Activities
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Two Levels of Design

Arch­ite­ctural Design
Broad design of the overall system structure
Also called General Design and Conceptual Design

Detailed Design
Low level design that includes the design of the specific program details
Design of each use case
Design of the database
Design of user and system interfaces
Design of controls and security

Abstract Three Layer Archit­ecture

Design the system interfaces

So other systems can talk to each other. System interfaces connect with other systems in many different ways:
- Save data another system uses
- Read data another system saved
- Real time request for inform­ation
- Software services

Relational Table Labelled

Components of design

Enviro­nment
Network and deployment archit­ecture
Applic­ation software
Server based apps, mobile devices, PCs. All components must itegrate as a functi­oning whole
User interface
Screens and reports o devices connected to the system
System interface
Comm interfaces between other automated systems
Database
Data struct­ures, deployment methods.
Security and controls
Firewalls, Access, data protection in transit between devices. External, internal checks and measures.

Logical design

abstract repres­ent­ation of the data flows, inputs and outputs of the system. This is often conducted via modelling. ER Modelling is commonly used.
 

Design Activities

Enviro­nment
have we spc in detail enviro­nment and options in which software will execute?
App archit­ecture and software
Detail spec elements of software and how each use case is executed
System interfaces
Spec how system will comm with all other systems inside and outside the org
User interface
Spec how users will interact with system to carry out all their tasks? (Use Cases)
Database
Spec in detail all info storage reqs
System controls and security
Spec elements to ensure system and data are secure and protected

Design the user interfaces

Dialog design begins with requir­ements, so use Use case flow of activi­ties, etc
Consid­era­tions:
- Workflow
- Dialogs
- Form Layout
- Look and feel
- Multiple interfaces (s/w, web, mobile)
- Multiple devices (laptop, touch, phone)
To the user, the interface is the system!

Systems Design

Process of defining and developing systems to satisfy specified requir­ements of the user.
Object­-or­iented analysis and design methods are becoming most widely used.
UML standard language in object­-or­iented analysis and design. Widely used for modeling software systems & increa­singly used for high designing non-so­ftware systems and organi­zat­ions.

Physical design

Relates to the actual input and output processes of the system. How data is input into a system, how it is verifi­ed/­aut­hen­tic­ated, how it is processed, and how it is displayed as In Physical design, the following reqs about the system are decided:
1. Input requir­ement
2. Output requir­ements
3. Storage requir­ements
4. Processing Requir­ements
5. System control and backup or recovery.

Physical portion of systems design can generally be broken down into three sub-tasks: User Interface Design, Data Design, Process Design
 

Design the applic­ation archit­ecture and software

1. Partition system into subsys­tems.
2. Define software archit­ecture. Three layer or model-­vie­w-c­ont­roller
3. Detailed design of each use case: Design class diagrams, Sequence diagrams, State machine diagrams

Design Class Diagram

Issues when consid­ering hosting

Reliab­ility, security, physical facili­ties, staff, potential for growth

Design the Database

Archit­ecture: distri­buted or central
Schema: Tables and columns in relational
Refere­ntial integrity constr­aints: Foreign key references – for linking tables
Uses domain model class diagram (or ERD)

Design the security and system controls

User interface controls
User Author­ization
Applic­ation controls
Transa­ctions are “atomic”
Database controls
No database anomalies
Network controls
Firewalls, access

Archit­ectural design

The archit­ectural design of a system emphasizes on the design of the systems archit­ecture which describes the structure, behavior, and more views of that system and analysis.

Design models (primary)

Package diagrams
Nodes and locations diagrams
Design class diagrams
Sequence Diagrams
Database Schema
User interface screens and reports
System and security controls
Commun­ication diagrams

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