Hierarchical Architecture

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

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

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

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

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

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

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

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

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

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

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

<<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

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

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

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

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

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

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

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

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

Example 1 1 min

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