Architecture & Applications

• Application Architectures
  • Application Perspective
  • Complex Applications
  • Generic Application Architectures
  • Use of Application Architectures
  • Application Types
• Batch/Data Processing Systems
  • Input-process-output
• Transaction Processing Systems
  • Transaction processing middleware
  • Information Systems Architecture
  • Resource Allocation Systems
  • Resource Allocation Architecture
  • E-Commerce System Architecture
• Event Processing Systems
  • Editing Systems
  • Editing System Architecture
  • Information and Resource Management Systems
• Language Processing Systems (Compilers)
  • Language Processing Components
• Conclusion

  Application Architectures

  Application Perspective

• So far had architectural perspectives on issues such as overall control, distribution and system structuring
• Now an alternative approach: architectures from an application perspective, i.e.: various application types
  • Two fundamental models of business systems
    • Batch processing
    • Transaction processing
  • Event processing systems
  • Language processing systems

    Complex Applications

• Follow a hybrid architectural model:
  • Different parts of the application structured in different ways
  • Different architecture models for individual subsystems
• Integrated within an overall system architecture

  Generic Application Architectures

• Application systems are designed to meet an organisational need
• As businesses have much in common, their application systems also tend to have a common architecture that reflects the application requirements
• A generic architecture is configured and adapted to create a system that meets specific requirements

  Use of Application Architectures

• As a starting point for architectural design
• As a design checklist
• As a way of organising the work of the development
• As a means of assessing components for reuse
• As a vocabulary for talking about application types

  Application Types

• Data Processing Applications
  • Data driven application that process data in branches without explicit user intervention during the processing
    • Billing systems; payroll systems
• Transaction processing applications
  • Data centred applications that process user requests and update information in a system database
    • E-commerce systems; reservation systems
• Event processing systems
  • Applications where system actions depend on interpreting events from the system’s environment
    • Games; word processors; real-time systems
• Language processing systems
  • Applications where the users’ intentions are specified in a formal language that is processed and interpreted by the system
    • Compilers, command interpreters

      Batch/Data Processing Systems

• Data-centred systems where the databases used are usually orders of magnitude larger than the software itself
• Data is input and output in batches
  • Input - a set of customer numbers and associated readings of an electricity meter
  • Output - a corresponding set of bills, one for each customer number
• Data processing systems usually have an input->process->output structure

  Input-process-output

• Input component reads data from a file or database, checks if validity and queues the valid data for processing
• Process component takes a transaction from the queue (input), performs computations and creates a new record with the results of the computation
• Output component reads these records, formats them accordingly and writes them to the database or sends them to a printer

Transaction Processing Systems

• Process user requests for information from a database or or requests to update the the database
• From a user perspective a transaction is:
  • Any coherent sequence of operations that satisfies a goal
  • For example - find the times of flight from London to Paris
• Users make asynchronous requests for service which are then processed by a transaction manager

Transaction processing middleware

• Transaction management middleware or teleprocessing monitors handle communications with different terminal types (e.g.: ATMs and counter terminals), serialises data and sends it for processing
• Query processing takes place in the system database and results are sent back through the transaction manager to the user’s terminal

Information Systems Architecture

• Information systems have a generic architecture that can be organised as a layered architecture
• Layers include
  • The user interface
  • User communications
  • Information retrieval
  • System database

Resource Allocation Systems

• Systems that manage a fixed amount of some resource (football game tickets, books in a bookshop, etc) and allocate this to users
• Example of resource allocation systems
  • Timetabling systems where the resource being allocated is a time period
  • Library systems where the resource being managed is books and other items for loan
  • Air traffic control systems where the resource being managed is the airspace

    Resource Allocation Architecture

• Resource allocation systems are layered systems that include
  • A resource database
  • A rule set describing how resources are allocated
  • A resource manager
  • A resource allocator
  • User authentication
  • Query management
  • Resource delivery component
  • User interface

E-Commerce System Architecture

• E-commerce systems are Internet-based resource management systems that accept electronic orders for goods or services
• Usually organised using a multi-tier architecture with application layers associated with each tier

Event Processing Systems

• These systems respond to events in the system’s environment
• Their key characteristics is that event timing is unpredictable so the architecture has to be organised to handle this
• Many common systems such as word processors, games, etc. are event processing systems

  Editing Systems

• Common type of event processing system
• Editing system characteristics
  • Single user systems
  • Must provide rapid feedback to user actions
  • Organised around long transactions so may include recovery facilities

    Editing System Architecture

• Editing systems are naturally object-oriented
  • Screen - monitors screen memory and detects events
  • Event - recognises events and passes them for processing
  • Command - executes a user command
  • Editor data - manages the editor data structure
  • Ancillary data - manages other data such as styles & preferences
  • File system - manages file I/O
  • Display - updates the screen display

Information and Resource Management Systems

Language Processing Systems (Compilers)

• Input a natural or artificial language and generate another representation
  • Programming language to machine code
• May interpret code and execute it
• Used when the easiest way to solve a problem is implement an algorithm
• Als used for domain-specific languages
  • What is that?

Language Processing Components

• Lexical analyser (tokenizer, scanner) - produces tokens: the words in the language, e.g.: variable names, operators, etc,
• Symbol table - stores the words
• Syntax analyser - parses tokens to produce a syntax tree, checks that tokens conform to the rules of the language
• Syntax tree - stores the program
• Semantic analyser - check aspects not related to syntactic form, e.g.: type correctness
• Code generator - transform and optimise the syntax tree into instructions for the target machine
  • Can think of it as a python filter process

Can also think of it as a Repository model of a compiler, where the repository handles the syntax definition and symbol table, output definition etc - as follows:

Conclusion

• Generic models of application architectures help us understand and compare applications
• Important classes of application are data processing systems, transaction processing systems, event processing systems and language processing system
  • Or a combination
• Data processing systems operate in batch mode and have an input -> process -> output structure.
• Transaction processing systems allow information in a database to be remotely accessed and modified by multiple users
• Event processing systems respond to events in the environment
• Language processing systems translate texts from one language to another and may interpret the specified instructions
• Typescript -> Javascript