INFO 355Week #61 Systems Analysis II Essentials of design INFO 355 Glenn Booker

Overview  Design bridges between requirements analysis and implementation of the system, hence it’s stunningly important Design generates a blueprint for the construction of the system  Design is heavily influenced by the devices to be used at the user or server ends of the system INFO 355Week #62

Types of devices  What kinds of devices might you expect for: A standalone application? A web app? A client/server app? A cloud app? A many-tiered client/server app? A client in an industrial setting? INFO 355Week #63

Network diagram  A simple network diagram can show the types of devices and servers in a system, and how they are connected (p. 157)  This forms the basis for design of each of the devices, servers, and interfaces among them Basic design principle: take a large problem and break it into smaller pieces INFO 355Week #64

Network diagram INFO 355Week #65

Levels of design  As we’ve hinted already, design can be broken into levels High level design = architectural design = general design = conceptual design Asks ‘what are the major pieces and structure of the system?’ Low level design = detailed design Asks ‘what is the design of each piece of the system?’ INFO 355Week #66

Design models  Design takes place by developing models of key parts of the system  Most models are diagrams with written descriptions  In OOAD, design models can include class, sequence, activity, package, and state INFO 355Week #67

Life cycle core processes  Throughout iterative development, each iteration includes some amount of several activities Identify problem and obtain approval Plan and monitor the project Discover and understand details Design system components Build, test, & integrate components Finish system tests and deploy solution INFO 355Week #68

Design system components  Within the step to design system components, it includes Design the environment Design app architecture and software Design user interfaces Design system interfaces Design the database Design system controls and security INFO 355Week #69

Design the environment  The system’s environment includes the hardware and supporting software needed for it to run Computing devices, OS, middleware, I/O and networking, etc. What equipment is needed? How do they communicate? INFO 355Week #610

Design app architecture and software  How is the app software structured?  What subsystems are needed?  How are data, logic, and presentation functions separated?  Where and how will users access the system?  Various diagrams might capture this information INFO 355Week #611

Design user interfaces  What devices will users use to access the system? Do we have a 4” screen or 30”? Graphical, touch or text interface?  How will the system support the user meeting their needs? How can the app be efficient and attractive? Make storyboards, prototypes, etc. INFO 355Week #612

Design system interfaces  How does the system communicate with other systems? Legacy systems, Google Maps, online data sources, vendors, suppliers, etc.  In what form is data exchanged? Text, binary, zipped, markup languages  Real time or asynchronous exchange? INFO 355Week #613

Design the database  Define the data model  Assess performance needs  Assess security needs  Assess privacy concerns  Redundancy?  Integration with existing databases? INFO 355Week #614

Design system controls and security  Consider security needs Physical and electronic security Internal and external threats Deliberate and accidental threats Legal and regulatory constraints Logging transactions, backup INFO 355Week #615

Revisit Design the Environment  Consider when we looked at the types of devices for various architectures  Major design choices depend on whether the app is designed for Internal deployment only External deployment only Internal and external deployment (remote or distributed environments) INFO 355Week #616

Internal deployment only  Stand-alone apps Rare, no Internet or other connections  Internal network-based systems Used only within the organization, e.g. client/server architecture over a LAN Could still be a desktop app or browser-based app INFO 355Week #617

Internal deployment only  Three-layer client/server Uses view, controller (business logic or domain), and data layers INFO 355Week #618

External deployment only  All Internet-based approaches  Configuration Also a 3-layer architecture (client/browser, web or app server, data server) Gives high accessibility, low cost, and uses common standards Challenges include security (HTTPS or TLS), throughput (server farms, CDN), and changing client software INFO 355Week #619

External deployment only  Hosting for Internet Based on needs for reliability, security, physical facilities, staffing, growth Might share colocation facility Purchase managed services Lease virtual servers Cloud computing (buy capacity as needed, per SLA) INFO 355Week #620

Internal and external deployment  Mixing internal and external deployments gets messy WANs are history Might use VPN for remote users Or use home server to authorize a peer-to-peer connection Diversity of clients is a challenge INFO 355Week #621