Transcript Virtual Gloves

Component architecture
Chapter Twenty
by Vanilson Burégio
Cin/UFPE
Component Architecture
Basis of any large-scale and is of utmost importance
for component based systems
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Defines:
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interaction between components and their environment
roles of components
It is not clear what a component architecture should
look like
The chapter presents na attempt at conceptualizing the
component architecture
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establish order within chaos
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The roles of an architecture
The basis for:
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Independence – enable multiple sources of solution parts
Cooperation – essential when the whole is more than the sum of
its parts
Technically
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Defines overall invariants
Include all policy decisions
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Roles of components
Enable interoperation across otherwise independent uses of
the mechanisms
Prescribe proper frameworks
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Limiting the degrees of freedom to curb variations and enable
cooperation
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The roles of an architecture
Principal considerations:
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Functionality
Performance
Reliability
Security
Commonly, these aspects are
ignored, emphasizing functionality.
The consequences can be fatal!
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Conceptualization – beyond
objects?
Conceptual level
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Useful to introduce layers
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To single out components
Separate concerns
Challenge: granularities
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Distinguish relationships between objects
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“has a” relationship - representative objects
“uses a” relationship
 can introduce cyclical dependencies
Relationship can be modeled as graphs
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Definitions of key terms
Component system architecture: consists of a set of
platform decisions, a set of component frameworks, and an
interoperation design
Component framework: is a dedicated and focused
architecture
Interoperation design: rules of interoperation among all
the frameworks joined by the system architecture
Component: a set of simultaneously deployed atomic
components
Module: a set of classes and possibly non-object-oriented
constructs (procedures, functions, …)
Resource: a “frozen” collection of typed items
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externalized immutable objects
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A tiered component
architecture
Fundamental notion of traditional software
architecture
Layer Vs Tier
Component
framework
Component
Component system
A multilayer architecture with 3 tiers- components,
component frameworks, a component system
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Components and middleware
Middleware:a set of software that sits between various
operating systems and a higher, distributed programming
platform
 Isolated middleware are slowly disappearing
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message queuing systems, transactions processor
monitors…
Emerging: specialized servers
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Application servers
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Integration servers
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Combine application management, data transaction, load
balancing, and other functions
Combine protocol conversion, data translation, routing, and
other functions
All these server categories introduce their own component
framework usually build on top of one of the component
platform
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Components Vs generative
programming
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Generative programming
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Go beyond such traditional transformation (fixed
transformer: compilers, JIT compilers)
Allows programmer to define new transformer
One approach (Czarnecki and Eisenecker - 2000)
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C++ templates
In a world of deployable components…
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Produce individual components
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Useful for large components or to produce a large numbers of
related components
Enhance composed systems
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Should not interfere with the unit of deployment characteristic
of components
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Component Frameworks
Chapter Twenty-one
by Vanilson Burégio
Cin/UFPE
Component Frameworks
Definition
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Software entity that support components conform to
certain standards and allows instances of these
components to be “plugged”
Roles
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Establishes environmental conditions for the component
instances
Regulates the interactions between components
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Enforce polices
Have taken off in a particular area:
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Contextual composition
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Contextual composition
Higher-order component framework seem
necessary and unavoidable
Compositional reasoning (Szabo, 1969)
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Well-formed Context
Elements declare their constraints (properties) on
acceptable context
The application of composition operators successively
builds contexts
Example:
C |- x:int C|-y:int
________________
C |- (x == y): bool
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Contextual composition
The compositional reasoning can be applied to
composition at all level of abstraction or granularity
For component software (at the level of component framewoks)
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Elements composition: instances created by components
composition operators: combines sets of such instances
Context: collect sets of instances into domains of
comparable properties
Component Framework: mechanism that supports
contextual composition of components
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There are various academic roots to the approach of using
contextual composition in software
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Contextual component
Frameworks Vs connectors
Architecture Description Language (ADL)
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Distinguish components and connectors
State which connectors should support
interaction between which components
Components
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Provide functionality
Connectors
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Focus on connectivity
Deal with aspects and system qualities
Substantial complexity
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Contextual component
Frameworks Vs connectors
Pure connection-oriented approach
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Components are restricted to only interact with other
components if connected appropriately
Contextual component Framework
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Can then be used to reintroduce the intercepting behavior
of connectors
Contexts themselves are not instances of components
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Non-generic aspects are provided by parametrizing generic
contexts with objects
ADLs
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Earlly ADLs were restricted to static connectivity
Later ADLs added support for dynamic connectivity and
dynamic reconfiguration
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COM+ contexts
COM
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Separate objects by threading model
MTS contexts
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Separate objects by transactional domain
COM +
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Unified these two notions and also a large
number of new context properties
Two objects are in the same domain if they
share a compatible set of context properties
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COM+ contexts
Example
C1
C2
V
X
W
U
C3
Transaction domain
Load-balancing domain
(TxID=42)
(RsrcID=7)
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EJB containers
Provides containers for EJB instances
Allow a class to be attributed to request explicit
transaction control
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Explicit control makes these classes much harder to
compose
Enable a easier path when wrapping legacy transaction
Support persistent objects
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Session
Entity
MDB
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CCM containers
CORBA Component Model
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Builds on EJB concepts
Adds support for process components to the session
and entity EJB components
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CCM session components => stateful session beans in EJB
CCM Service components => stateless session beans in EJB
Instances of a process component have persistent state
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Tuple and object spaces
An approach of contextual composition
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Based on the concept of an omnipresent data space that can e
used to communicate without explicit addressing
Linda coordination language (1988)
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Introduced Tuple spaces
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Three operations
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Spaces that hold atoms of data called tupes
Adding a tuple to a space
Matching and reading (polling) a tuple in a space
Matching and removing a tuple from a space
JavaSpaces
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java.sun.com/products/javaspaces
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BlackBox component
Framework
Part of the BlackBox component builder, a
component-oriented programming environment
(Oberon microsystems - 1997)
Focus
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Visual components
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Components for compound-document-based client applications
with rich graphical user interface
The framework
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Consists of a core set of layered modules and a open
set of subsystems
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BlackBox component
Framework
Based in the following patterns and approaches:
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Carrier-rider-mapper design pattern
Directory objects
Hierarchical model view separation (HMVC)
Container modes
Cascade message multicasting services
…
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Portos
A realtime operating system of components
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New components can be loaded ate runtime
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Various configurations ar possible
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PortosLoader
At least the modules PortosKernel and PortosTasks are
required
PortosTasks is the central module of Portos
JBed - a Java version of Portos
Portos IDE
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Cross-development environment for developing Portos
applications
Extension of the BlackBox component builder
Adds functionality for transfer of code files and data to and from
an embedded systemCIn/UFPE
running Portos