CHAPTER 7. HIERARCHICAL ARCHITECTURE
7.1. Main-Subroutine Architecture
The purpose is to reuse the subroutines
Data location
In the classical procedural paradigm
With object orientation,
the data is encapsulated in each individual object so that the information is protected.
a software system is decomposed into subroutines hierarchically
The hierarchy will be refined according to the desired functionality of the system.
Refinements are conducted vertically until
The decomposed subroutine is simple enough to have its sole independent responsibility
Whose functionality may be reused and shared by multiple callers.
A Data Flow Diagram (DFD) is often used to model the software requirement
A transform flow is mapped by a controlling module for incoming, transform and outgoing information processing
A transaction center is located at the fork origin of action paths.
Benefits
Easy to decompose
This architecture can still be used in a sub-system of OO Design.
Limitations
Globally shared data in classical main-subroutines introduces vulnerabilities
Tight coupling may cause more ripple effects of changes
7.2. Master-Slave Architecture
Is a variant of the main-subroutine architecture style supports
fault tolerance
system reliability
The master selects a particular service result among slaves by certain selection strategy.
The slaves may perform
the same functional task by
totally different functionality.
different algorithms
different methods
Applicable Design Domains
Used for the software system where the reliability is critical.
Also use the term master-slave or parent-child relationship in database schema design
to specify the dependency of one entity on another.
If the master node is deleted then the slave node does not have any reason to stay.
7.3. Layered Architecture
The system is decomposed into a number of higher and lower layers in a hierarchy
The interface of each layer encapsulates
all detailed service implementations in
the current layer
the interfaces of the layers below.
A request from higher layer to the layer below is made via
method invocation
the response goes back up via
method return
A simple software system may consist of two layers:
Interaction Layer
The Processing layer
The Interaction layer provides
User Interfaces to clients
Takes requests
Validates and Forwards request to processing layer for processing
Responds to clients
Gets the forwarded requests
Performs business logic process
Accesses database
Returns the results to its upper layer
Lets upper layer respond to clients
Applicable Design Domains
Any system that can be divided
Application specific portions
Platform specific portions which provide generic services to the application of the system.
Applications that have clean divisions between
Core services
Critical services
User interface services, etc.
Applications that have a number of classes that are closely related to each other
Benefits:
Incremental software development
Enhanced independence of upper layer to lower layer
Enhanced flexibility
Component-based technology is a suitable technology to implement the layered architecture
Promotion of portability
Limitations:
Lower runtime performance
Conflict of interlayer communication may cause deadlocks
bridging” may cause tight coupling
Exceptions and error handling is an issue
7.4. Virtual machine
Is built up on an existing system
Provides a virtual abstraction
a virtual machine looks like emulation software
In most cases,
A virtual machine separates a programming language or application environment from a execution platform
Applicable Domain:
Suitable for solving a problem by simulation or translation if there is no direct solution.
Sample applications include
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 software development.
Simulation for disaster working model.
Limitations:
Slow execution of the interpreter due to the interpreter nature.
Additional overhead due to the new layer.