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)