What is Systems Design

\text{Analysis (Analysis Models and Documents)} \to \text{Design (Design Models and Documents)} \to \text{Implementation}

• Analysis: What is required
  • Starting point for design
• Design: How the system will be configured and constructed.
  • Starting point for implementation
  • Objective: Define, Organize, and Structure the components of the solution to serve as a blueprint for construction.

Design Models

Design is a model-building activity.

• A project’s formality dictates the type, complexity, and depth of models.
  • (e.g., AGILE/Iterative projects typically build fewer models.)

Remember: Jumping to programming without design often causes less than optimum solution and may require rework.

Analysis Models \to Design Models

Requirements Models:

• Domain Model Class Diagram
• Use Case Diagrams
• Activity Diagrams and Use Case Description
• System Sequence Diagrams
• Requirements State Machine Diagrams

Design Models:

• Component Diagrams
• Deployment Diagrams
• Design Class Diagrams
• Interaction Diagrams (Sequence Diagrams)
• Design State Machine Diagrams
• Package Diagrams

Design Activities

Design Activities:

• Describe the environment (all the tech required to support the software application)
  • How will this system interact with other systems and existing tech?
• Design…:
  • Application Components (well-defined units of software the perform function(s))
    • What are key parts of the information system, and how will they interact when the system is deployed?
  • User Interface (to the user, the UI is the system)
    • How will users interact with the information system?
  • Database
    • How will data be captured, structured, and stored for later use by the information system?
  • Software Classes and Methods (aka: detailed design)
    • What internal structure for each application component will ensure efficient construction, rapid deployment, and reliable operation?
    • (e.g., Design Class Diagram, Sequence Diagrams, State-Machine Diagrams)

More on Application Components: Issues packaging components

• Scope and size: What are the functions, boundaries, and interfaces?
• Programming Language: What are the accepted languages?
• Build of Buy: Is an acceptable version available to purchase?

More on Application Components: Typical models for designing application components

• Package Diagram
• Component Diagram
• Deployment Diagram

More on UI: Typical models for designing UI

• Storyboard
• System sequence diagram
• Small screen menu prototype

More on Database: Relational Database Management Systems (RDBMS)

• Current tech frequently uses RDBMS.
• Requires converting the data model to a relational database.
  • Must address:
    1. Throughput and response time
    2. Security.

More on Database: Example — Typical Table Definition as Part of Database Scheme

Field	Type	Collation	Attributed	Null	Default	Extra
productItem	varchar(15)	latin1_swedith_ci		No	None
inventoryItem	mediumint(9)			No	None
size	varchar(8)	latin1_swedith_ci		No	None
color	varchar(10)	latin1_swedith_ci		No	None
options	varchar(12)	latin1_swedith_ci		No	None
quantityOnHand	mediumint(9)			No	None
averageCost	decimal(8,2)			No	None
reorderQuantity	mediumint(9)			No	None
dateLastOrder	date			No	None
dateLastShipment	date			No	None

System Controls and Security

Integrity Controls: Maintain integrity inf inputs, outputs, and data and programs.

• Integrated into application programs and DBMS
• Objectives:
  • Ensure only appropriate and correct business transactions are accepted.
  • Ensure transactions and recorded and processed correctly.
  • Protect and safeguard assets like the database.

Security Controls: Protect the assets form threats, internal and external.

Input Controls

Prevent invalid or erroneous data from entering the system.

Value Limit Controls: Check the range of inputs for reasonableness

Completeness Controls: Ensure all the data has been entered

Data Validation Controls: Ensure that specific data values are correct

Field Combination Controls: Ensure data is correct based on relationships between fields.

Output Controls

Important for ensuring that output arrives at proper destination and is accurate, current, and complete.

Examples:

• Physical access to printers and display devices.
• Protection from “dumpsite diving” discarded data
• Labels on printed and electronic output to identity source of data.

Redundancy, Backup, and Recovery

Goal: Protect data and systems from catastrophes.

• e.g., databases, hardware, software applications, networks.

Designing Security Controls

Goal: Protect all assets against external threats.

• Protect and maintain a stable, functioning operating environment 24/7
• Protect information and transactions during transmission across networks and Internet.

Types of Users

Access Controls: Limit a person’s ability to access servers, files, data, and applications.

Registered Users: Those with authorization.

Unauthorized Users: Anyone not registered

Privileged Users: Those that maintain lists and systems.

Data Encryption

Encryption: Alter data to make it unrecognizable.

Decryption: Convert encrypted data back to readable format.

Encryption Algorithm: Mathematical transformation of the data.

Encryption Key: Lone data string that allows the same algorithm to produce unique encryptions.

Symmetric v.s. Asymmetric Key Encryption

Symmetric: Uses same key to encrypt and decrypt

Asymmetric: Uses different keys to encrypt and decrypt.

Secure Transactions

Secure Sockets Layer (SSL): Standard set of protocols for authentication and authorization

Transport Layer Security (TLS): Internet standard equivalent to SSL.

IP Security (IPSec): Internet security protocol at a low-level transmission.

Hypertext Transfer Protocol Secure (HTTPS): Internet standard to transmit Web pages.