System sequence diagram
Concept of System Sequence Diagram (SSD)
Part of system design. Communicates to OO programmers.
SSD shows interaction between actors and system (global SSD), and among objects (detailed SSD)
SSD specifies flow of data (messages)
Messages are actions (resemble commands) invoked on destination object
Global SSD
SSD of a customer order system
Figure 6-14
Global SSD – loops
Figure 6-15
True/FalseCondition
Input
Expected output
Loop
Note: extendedPrice = price * quantity
Creating global SSD
1. Start with an activity diagram and/or use case description.
2. Identify the input messages from actor to system. For figuring attributes (input parameters), use class diagram.
3. Identify/apply special conditions (iteration) to input messages, if any.
4. Identify output messages.
Creating global SSD (cont.)
Figure 6-16. Activity diagram of Create New Order use case, Telephone Scenario at RMO
Figure 6-17. Global SSD of the same Figure 5-31 (detail). Class diagram of RMO
AccountaccountNocustomerID
ProductproductIDsizedescription
CatalogcatalogID
CatalogProductprice
OrderorderIDTotalAmt
OrderDetaiquantityextendPrice
Holycross of Davao CollegeSystem Analysis and Design (IT11)By: John Ely P. Masculino
Designing System InterfacesDesigning System Interfaces (UI Vs SI)(UI Vs SI)
System Interface (SI) - I/O with minimal or no human intervention.
User Interface (UI) - I/O requiring human interaction.- User interface is everything end user comes into contact with while using the system- To the user, the interface is the system
Identifying System InterfacesIdentifying System Interfaces
- Inputs from other System (messages, EDI).- Highly automated inputs such as scanners.- Inputs that are from data in external
databases.- Outputs to external databases.- Outputs with minimal HCI.- Outputs to other systems.- Real-time connection (both input and output).
The full range of inputs and The full range of inputs and outputs in an information systemoutputs in an information system
Designing System InputsDesigning System Inputs
- Identify devices and mechanisms• High-level review of most up-to-date methods
to enter data
- Identify all system inputs and develop list of data content of each
• Provide link between design of application software and design of user and system interfaces
- Determine controls and security necessary for each system input
Input Devices and MechanismInput Devices and Mechanism
- Capture data as close to original source as possible- Use electronic devices and automatic entry whenever possible- Avoid human involvement as much as possible- Seek information in electronic form to avoid data reentry- Validate and correct information at entry point
Prevalent Input Devices to Avoid Human Data Entry
- Magnetic card strip readers- Bar code readers- Optical character recognition readers and scanners- Radio-frequency identification tags- Touch screens and devices- Electronic pens and writing surfaces- Digitizers, such as digital cameras and digital audio devices
Defining the Details of System InputsDefining the Details of System Inputs
- Ensure all data inputs are identified and specified correctly
• Identifying user and system inputs with OO approach has same tasks as traditional approach
• OO diagrams are used instead of DFDs and structure charts
• System sequence diagrams identify each incoming message
• Design class diagrams and sequence diagrams identify and describe input parameters and verify characteristics of inputs
Partial System Sequence Diagram for Payroll System Use Cases
System Sequence Diagram for Create New Order
Input Messages and Data Parameters from RMO System Sequence Diagram
Designing System OutputsDesigning System Outputs
- Determine each type of output- Make list of specific system outputs required based on application design- Specify any necessary controls to protect information provided in output- Design and prototype output layout- Ad hoc reports – designed as needed by user
Defining the Details of System Outputs
Outputs indicated by messages in sequence diagrams– Originate from internal system objects– Sent to external actors or another external
system
Output messages based on an individual object are usually part of methods of that class object
To report on all objects within a class, class-level method is used that works on entire class
Table of System Outputs Based on OO Messages
Types of reportsTypes of reports
– Printed reports– Electronic displays– Turnaround documents– Graphical and Multimedia presentation
Types of Output ReportsTypes of Output Reports
Detailed– Contains detailed transactions or records
Summary– Recaps periodic activity
Exception– Only contains information about nonstandard
conditions
Executive– Summary report used for strategic decisions
Designing Integrity Controls
Mechanisms and procedures built into a system to safeguard it and information contained within
Integrity controls– Built into application and database system to
safeguard information
Security controls
Objectives of Integrity Controls
- Ensure that only appropriate and correct business transactions occur- Ensure that transactions are recorded and processed correctly- Protect and safeguard assets of the organization
• Software• Hardware• Information
Points of Security and Integrity Controls
Input Integrity Controls
– Used with all input mechanisms– Additional level of verification to help
reduce input errors– Common control techniques
• Field combination controls• Value limit controls• Completeness controls• Data validation controls
Database Integrity Controls
– Access controls– Data encryption– Transaction controls– Update controls– Backup and recovery protection
Output Integrity Controls
– Ensure output arrives at proper destination and is correct, accurate, complete, and current
– Destination controls - output is channeled to correct people
– Completeness, accuracy, and correctness controls
– Appropriate information present in output
Integrity Controls to Prevent Fraud
Three conditions are present in fraud cases– Personal pressure, such as desire to maintain
extravagant lifestyle– Rationalizations, including “I will repay this money”
or “I have this coming”– Opportunity, such as unverified cash receipts
Control of fraud requires both manual procedures and computer integrity controls
Fraud Risks and Prevention Techniques
Designing Security Controls
Security controls protect assets of organization from all threats– External threats such as hackers, viruses, worms,
and message overload attacks
Security control objectives– Maintain stable, functioning operating environment
for users and application systems (24 x 7)– Protect information and transactions during
transmission outside organization (public carriers)
Security for Access to Systems
Used to control access to any resource managed by operating system or network
User categories– Unauthorized user – no authorization to
access– Registered user – authorized to access
system– Privileged user – authorized to administrate
system
Organized so that all resources can be accessed with same unique ID/password combination
Users and Access Roles to Computer Systems
Managing User Access
Most common technique is user ID / password
Authorization – Is user permitted to access?
Access control list – users with rights to access
Authentication – Is user who they claim to be?
Smart card – computer-readable plastic card with embedded security information
Biometric devices – keystroke patterns, fingerprinting, retinal scans, voice characteristics
Data Security
Data and files themselves must be secure
Encryption – primary security method– Altering data so unauthorized users cannot view
Decryption– Altering encrypted data back to its original state
Symmetric key – same key encrypts and decrypts
Asymmetric key – different key decrypts
Public key – public encrypts; private decrypts
Symmetric Key Encryption
Asymmetric Key Encryption
Digital Signatures and Certificates
Encryption of messages enables secure exchange of information between two entities with appropriate keys
Digital signature encrypts document with private key to verify document author
Digital certificate is institution’s name and public key that is encrypted and certified by third party
Certifying authority– VeriSign or Equifax
Using a Digital Certificate
Secure Transactions
Standard set of methods and protocols for authentication, authorization, privacy, integrity
Secure Sockets Layer (SSL) renamed as Transport Layer
Security (TLS) – protocol for secure channel to send messages over Internet
IP Security (IPSec) – newer standard for transmitting Internet messages securely
Secure Hypertext Transport Protocol (HTTPS or HTTP-S) – standard for transmitting Web pages securely (encryption, digital signing, certificates)
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