1. Hierarchical Architecture

2. Objectives Introduce concepts of hierarchy arch. pros and cons
Main/subroutine
Master/slave
Layered architecture
Virtual machine
pros and cons
implementation techniques
1 min

3. Overview Key Idea: services layered
Upper layer consumes service from lower layer
Why? system too complex
1.5 min

4. Overview System SWs are typically – hierarchical architecture Examples
Microsoft .NET
Unix operating system
TCP/IP
1.5 min

5. General Rules
Services at lower level provides more specific functionality down to fundamental utility services such as
I/O services, transaction, scheduling, security services, etc.
Middle layers provide more domain dependent functions such as
Business logic, core processing, etc.
Upper layers provide more abstract functionality in the form of user interfaces such as
Command line interpreter, GUI, Shell programming
Plus Point:
Any changes to a specific layer may affect only its adjacent upper layers.
So, no ripple effects of change
1.5 min

6. Main/Subroutine Architecture
Probably the oldest and most widely used architecture.
Purpose:
Encourage re-use of modules
Idea
System decomposed into sub-routines
A “main” program calls sub-routines and accomplishes task
1 min

7. How Sub-routine Call is Supported
Function Call Supported by Assembly
Protect old register values by pushing to stack
Set parameters in register
Call the subroutine
Jump, Long Jump, Call instruction
Software Interrupt
Function Call Supported by High Level Language
Much more convenient
Much more tricky!
Parameter passing
Pass by value
Pass by reference
1.5 min

8. Main/Subroutine Design
Usually Requirement Spec. Specified in Data Flow Diagram (DFD)
Objective: Map from DFD to Main/Subroutine Design 1 2 3 4 5 7 6 8
Customer
record
Customer info
validate
return
Action path
1.5 min

9. DFD Two types of flow Mapping Process
Transform Flow: input data get processed and results in output data (sequential)
Transaction Flow: depending on input data, take different control actions (branch)
Mapping Process
Identify transform and transaction flows
Map each flow into a subroutine
Generally: a main process controls the overall flow
1.5 min

10. DFD mapped into main/subroutine structure#2 #1 #3 #4
#7-8
#5-6 #6 #5 #8 #7
Do it on board: 2 min
15.5 min now

11. Main/subroutine: Summary
Benefits:
Easy to decompose the system
Can still be used in sub-system of OO Design.
Limitation:
Globally shared data are vulnerable
Tight coupling may cause ripple impacts as compared to OO design
1.5 min
17 min now

12. Master-Slave A variant of main-subroutine architecture It supports
Fault tolerance and system reliability
In this architecture:
The slaves provide replicated services to the master
The master selects a particular result among slaves by certain selection strategies.
Slaves may perform the same functional task by different algorithms and methods or a totally different functionality.
1.5 min
17 min now

13. <<slaves>>
Master-Slave
Block diagram for master-slave architecture
Class diagram for master-slave architecture
Master
Slave 1
Slave 2
master
<<slaves>>
+service()
slave 2+
1.5 min
17 min now

14. Master-Slave Characteristics: Applicable domain:
Parallel computing and accuracy of computation
Applicable domain:
Where reliability is crucial
1.5 min
17 min now

15. Layered Arch. Idea: functionality grouped into layers
upper layer invokes func. in lower layer
0.5 min

16. Example Benefits: Mainly in system development and maintenance
(1) interface defined and published  concurrent development by multiple teams
(2) each layer is thoroughly tested  no deeply nested debugging
1.5 min

17. Physical Implementation
Functions in one layer usually organized in one package
Some times deployed as services
1 min

18. Examples OSI 7-layer Network Stack
OS (driver, kernel, system call, application)
Web service (ip, tcp, http, xml, SOAP, WSDL, BPEL, UDDI)
1.5 min

19. Summary - Layered Applicable Design Domains:
For systems that can be divided between portions providing generic services to the application of the system
For applications which have classes that are close related each other
0.5 min

20. Summary - Layered Benefits: Limitations:
Incremental software development
Enhanced independence of upper layer to lower layer
Enhanced reusability and interchangeability
Component-based technology is a suitable
Promotion of portability
Limitations:
Lower runtime performance
Many applications can not fit this architecture
Exception and error handling
2 min
24 min

21. Virtual Machine Variation of Layered Approach Idea:
Provide a virtual interpretation layer that separates
Application
Physical machine layer
i.e., Software/Components run on simulation layer
1 min

22. Example 1
1 min

23. Summary Applicable Design Domain: Benefits: Limitations:
Suitable for solving a problem by simulation or translation
Sample applications such as interpreters of microprogramming, XML processing, script command language execution, rule-based system execution, Smalltalk and Java interpreter typed programming language
Benefits:
Portability and machine platform independency
Simplicity of the software development
Simulation for non-native and disaster working model
Limitations:
Slow execution of the interpreter
Additional overhead due to the new layer
1.5 min