Architectures

1Intro

• Architectural Refinement

  • Domain > uses > Technical > uses > Platform

• Architecture > structures > Components

• architecture specifies "load carrying" components, not details

• makes complexity manageable

2Requirements

• should be

  • correct (users, stakeholders)

• implementable

• unambiguously defined

• testable

• levels

  • Oranization Level

• System Level

• Component Level

• Functional

  • Use Cases

• Non-Functional (Design Time, Runtime, Org Env)

3Principles

• (Loose) Coupling among

  • dependencies among components

• keep complexity of structures low

• increase changeability

• (High) Cohesion within

  • dependencies within a component

• component can be understood or changedwithout looking at other components

• Design for Change

  • plan for foreseeable changes

• consider requirements likely to arise

• Risks

  • more development time

• higher costs, memory, performance

• Separation of Concerns

  • Modularization vs "God Class"

• Requirements

• Complex Architecture Model into Views

• Organizational Responsibilities

• Aspect-Orientation...

• Information Hiding

  • hide implementation details behind an interface

• present only really necessary parts > Facade Pattern

• More

  • Abstraction - Explicit Interfaces, Segregation of Interface and Implementation

• Traceability, Self Documentation, Incremental Evolution

4Styles

• describe fundamental structures of a software system and its properties

• Component types +Topology + Connectors + Semantic constraints

• Examples

  • Dataflow Systems

    • Batch Sequential, Pipes and Filters

• Call-and-Return Systems

  • Main Prog, OO, Hierarchical Layers

• Independent Components

  • Communication, Event Systems, Implicit Invocation

• Virtual Machines

  • Interpreters, Rule-based Systems

• Data-Centered-Systems (Repositories)

  • DBs, Hypertext Systems, Blackboards

5Patterns

• Gang-of-Four Book Design Patterns

• reusable design expterise, time-proved solutions to commonly occuring problems

• also used for documentation and communication

• resolves/balances a system of forces (Memory, Costs, Performance, ...)

• describes consequences / positive negative

• Layers Pattern

  • problem

    • high- & low-level components decoupling

• solution

  • layer has same level of abstraction

• interface between layers

• Indirection Layer Pattern: wrap access

• Batch Sequential Pattern

  • problem

    • complex task, can be sub-divided

• solution

  • sub-steps separated

• call next sequential step

• processes batch of data per step

• Pipes and Filters Pattern

  • problem

    • flexibly compose individual sub-tasks

• solution

  • Filters

    • independent components

• Pipes

  • connectors, data buffers

• Shared Repository Pattern

  • problem

    • share data, sequential architectures

• common way: invocation parameters

• inefficient for large data sets

• information varies from invocation to invocation

• long-term persistence

• solution

  • central data store

• scaleable, consistent, transactions...

• Active Repository

  • registry of clients

• notification mechanisms

• Blackboard

  • heuristic computation by sub-tasks

• step-wise improvement

• control unit

6Patterns by Views

• Data Flow and Tranformation View

  • Pipes and Filters

• Batch Sequential

• Layered Decomposition View

  • Layers

• Indirection Layer

• Data Repository View

  • Shared Respository

• Active Respository

• Blackboard

• Adaptation Infrastructure View

  • Microkernel

    • system family, different versions

• services - internal / external servers

• Reflection

  • unanticipated changes

• meta level, meta-objects

• Plugin

  • extend, runtime environments without re-compile

• central (re-)config at runtime

• Interceptor

  • extend reusable services

• register for dispatchers > interceptor events

• Language Infrastructure View

  • Interpreter

    • parse/interpret language syntax / grammar at runtime

• scripts, portable to interpreter platform implementations

• simple eg: class per grammar rule

• Virtual Machine

  • portability, code optimization, no runtime interpretation req

• intermediary byte-code > VM implementation layer

• Rule-Based-System

  • logical problems hard to express, nested if-statements

• facts (data), rules (knowledge) + engine (application)

• Interaction Decoupling View

  • MVC

    • model, encapsulates data

• views, display data to the user

• controller, receives user input, transmits to the model

• Presentation-Abstraction-Control

• C2

• Explicit Invocation

  • couple client-supplier

    • performance

• direct communication

• block for result

• fixed topology

• direct invocation by service name and parameters

• synchronous, asynchronous

  • fire and forget (no response)

• sync with server (ack, no result)

• poll object (result)

• result callback (result notification)

• Implicit Invocation

  • de-couple client-supplier

    • unknown supplier

• results not needed yet

• dynamic client add/removal

• indirect invocation through

  • publish-subscribe

• message queuing

• broadcast

• Component Interaction View

  • Client-Server

• n-Tier Architectures

• Publish-Subscribe

• Peer-toPeer

• Distributed Communication View

  • Broker

    • hides communication complexity

• requestor, invoker, marshaller, request handler

• RPC

• Message Queuing

7Modeling

• Meta-models describe models > Modeling levels

• Modeling languages

  • meta-model = abstract syntax

• notation = concrete syntax

• informal description = semantics

• ADL

  • Architecture Description Languages

• readable, formal respresentation of architecture

• Components

  • functional + non-functional aspects via interfaces

• Connectors

  • component communication

• Configuration

  • of components and connectors

• eg: Acme, AADL, C2, Darwin, Wright

• UML

  • MOF Meta Object Facility

    • meta-meta model

• OMG levels

  • M3 MOF - EBNF-Formalism

• M2 UML - Java Grammar

• M1 UML Model A - Java Program P

• M0 instance A - Execution of Program P

• instrastructure + meta-model superstructure

• hard extension - meta-model, new UML language

• soft extension - profile (steoreotypes, tags, constraints)

8MDSD

• Model-Driven Software Development

• models as central artifacts

• domain-related for efficiency

• DSL

  • Domain Specific Languages

• tailor-made language for a specific problem domain

• specialized, expressive and easy to use

• embedded

  • extends General Purpose Language (GPL)

• often interpreted instead of generation

• external

  • different format than target language

• any syntax, not bound to host language or platform

• transformations map to target platform

• Code Generation

  • eg using templates

• alternative: interpreter

• Options

  • informal box-and-line diagrams

    • often not precise enough

• use existing ADL

  • often no ADL fits exactly

• use UML and extend UML meta-classes

  • tedious work

• custom architecture meta-model

  • glossary of architecture concepts

• clarifying

9Views

• make complex systems understandable

• different

  • stakeholders

• tasks

• abstraction levels

• 4+1 View Model

  • Use Case view

    • centric

• validates the others

• Logical view

  • describes system in terms of abstractions

• eg: class, sequence, collaboration diagrams

• Development view

  • structure of modules, files, packages

• eg: package diagram

• Process view

  • process communication

• eg: activity diagrams, process modeling languages

• Physical view

  • installation, exection environment

• eg: deployment diagrams

10Decisions

• strategic (long-term and significant), not operational

• form architecture

• steps

  • prepare > make > communication > realize > evaluate

• problems

  • decisions get lost in models

• Decision Modeling

  • template or meta-model

• capture key design issues, rationale

• conscious design decisions

• consider impact on NFRs and quality factors

11Organisational

• organisation culture defines values and norms

• sub-organisations, internationalization, outsourcing

• Organizational Patterns

• Agile Methods

• Individuals

  • influence collaboration

• require Social competences

• group

  • composition, heterogeneous

• experienced, cooperative moderator

• skills appointment

• one or two creative team members

• TOGAF

  • Generic Skills

• Business Skills and Methods

• Enterprise Architecture Skills

• Program or Project Management Skills

• IT General Knowledge Skills

• Technical IT Skills

• Legal Environment

12Prüfungsfragen

• Architecture decision modelling

• 4+1 View Modell

• Model Driven Software Development

  • Domain

• Domain Driven Design

• Domain Specific Languages

• MOF und UML

  • 4-Schichtige Modellierungsarchitektur des OMG

• Arten von Anforderungen bei Architekturen

• Architecture Modelling Options

• DSL

  • embedded vs external

• Patterns- problem- solution- comparison

  • Layer

• Batch Sequential

• Pipel and Filters