13. 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
16. 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.
17. Creating global SSD (cont.)
Account
accountNo
customerID OrderDetai
quantity
extendPrice
Order
orderID
TotalAmt
Product
productID
size
description
CatalogProduct
price
Catalog
catalogID
Figure 6-16. Activity diagram of Figure 6-17. Global SSD of the same Figure 5-31 (detail).
Create New Order use case, Class diagram of RMO
Telephone Scenario at RMO
18. Holycross of Davao College
System Analysis and Design (IT11)
By: John Ely P. Masculino
19. Designing System Interfaces
(UI Vs SI)
System Interface (SI) User Interface (UI)
- I/O with minimal or no - I/O requiring human
human intervention. interaction.
- User interface is
everything end user comes
into contact with while
using the system
- To the user, the interface
is the system
20. Identifying 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).
21. The full range of inputs and
outputs in an information system
22. Designing 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
23. Input 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
24. 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
25. Defining 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
29. Designing 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
30. 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
32. Types of reports
– Printed reports
– Electronic displays
– Turnaround documents
– Graphical and Multimedia presentation
33. Types 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
34. 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
35. 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
37. 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
39. 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
40. 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
42. 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)
43. 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
45. 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
46. 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
49. 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
51. 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)