Documenting Software Architectural Component and Connector with UML 2

KNOWLEDGECUDDLE PUBLICATION
International Journal of Computer Engineering and Science, August- 2014
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Documenting Software Architectural
Component and Connector with UML 2
Vikram M. Agrawal
IT Department
BVM Engineering College
agrawal.vm@gmail.com
_______________________________________________________________________________________
ABSTRACT: Earlierversions of the UML have been an out of depth for documenting software architectures
like component, port, connector and system. Users have adopted conventions for representing architectural
concepts using different grouping of UML modeling element. They can also create profiles to focus the UML.
Changes incorporated in UML 2 have improved UML’s suitability for software architectural documentation,
but UML is still an out of your depth for documenting some types of architectural information. In this paper,
there is description of documenting component and connector using UML but in particular case,
documenting architectural connectors and components remains problematic.
Keywords: - component, connector
_______________________________________________________________________________________
1. INTRODUCTION
The first work of stakeholder to create communicating architecture of whole system because
architectures are rational constructs of enduring and long-lived importance.Architecture must be clearly
explained because others are to build systems from it, analyze it, maintain it, and learn from it. Therefore,
increased attention is now being paid to how architectures should be documented.
Modern software architecture practice embraces the concept of architectural views as part of the
solution [1–4]. A view is a representation of a set of system elements and relations associated with them [5].
Systems are typically recognized in terms of many views, each of which represents aspects of the system needed
to analyze and communicate different quality attributes of the system. So we can consider the all the view of all
the stakeholders. For instance, a layered view is useful for understanding modifiability, while a communicating
processes view is useful for understanding system performance.
The widespread presence of UML has directed practitioners to try to use it to document software
architectures. The results have been mixed and somewhat unacceptable and un-useful. For example, UML has
no built-in way to represent the basic architectural concept of a layer. Nor was there any straightforward way to
represent a connector, in the rich sense proposed by Garlan and Shaw [6]. Nevertheless, ways have been
proposed to represent several familiar architectural views using UML. Previous work has investigated ways that
it can be used as is to represent architectural concepts or ways that UML can be specialized to improve its
suitability for architectural documentation, such as [7–9].
During the development of UML 2, changes were made that significantly improve UML’s suitability
for architectural documentation [10]. Structured Classifiers permit improved representation of architectural
hierarchy, often used effectively to represent detail in stages or for different USERS. Ports provide a normal
way to represent runtime points of interaction and collections of interfaces involved in a common protocol.
Unfortunately, some of UML’s drawback with respect to architectural documentation remain. In this
paper, we examine one such drawback of documenting architectural connector with UML 2. Though UML 2
provides better support for representing connectors, users are still left with a variety of modeling options to
choose among, each of which is best suited to different uses.
To distinguish between architectural and UML uses of the same term, we capitalize the names of UML
modeling elements (e.g., Component or Class) and use lower case for architectural concepts (e.g., component or
connector).

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2. COMPONENT AND CONNECTOR VIEWS
Component and connector views present architecture in terms of elements that have a runtime presence
(e.g., processes, clients, database,and data stores) and trails of interaction e.g., communication links and
protocols, information flows, use of resources, and access to common resources. Components are the major
units of run-time interaction or data storage. Connectors are the interaction mechanisms among components.
Different styles of Component and Connector views important vocabulary and often impose additional
topological restrictions. In a shared data view, the data repository and the accesses are the components; the
access mechanisms are the connectors. And in a client-server view, the components are clients and servers; the
connectors are the protocol mechanisms by which they interact.
When considering documentation options it is important to be clear about criteria for choosing one way
of using UML 2.0 over other possibilities. These criteria allow us to determine when a particular documentation
option is likely to be appropriate. The criteria (the first three of which are derived from [8]) are
 Semantic match: The UML modeling elements should map naturally to the architectural concepts that
are being documented.
 Visual clarity: The UML description should bring conceptual clarity to a system design, avoid visual
disorder, and highlight key design information.
 Completeness: All relevant architectural features for the design should be implemented in the UML
model.
 Tool support: Not all uses of UML are equally supported by all tools, particularly when specialize the
UML.
The changes in UML 2 provide better representation options for many architectural concepts with respect to
these criteria, particularly in terms of semanticoptions for architectural connectors remain deficient. Ideally, we
look for a UML modeling option that is
 Typically used to represent trails of interaction,
 visually separate from component representations and introduces a minimum number of visual
elements,
 able to represent connector behavior e.g., a state machine, state e.g., queue size, and interfaces over
which a connector’s rules might be imposed, and
 supported by UML tools implementing the minimal features needed to be compliant with the UML 2
standard.
3. DOCUMENTING COMPONENTS AND CONNECTORS WITH UML 2
In this section, ways of using UML (class diagram in particular) to document component and connector
view are described. Following elements of component and connector view will be described using UML:
components and component types, connectors and connector types, ports, roles, systems and properties [8].
Since there is no best way of documenting these elements using UML, multiple alternatives will be
presented, along with their advantages and disadvantages. Architectural descriptions which are produced this
way should respect documented UML semantics and the intuitions of UML modelers. The interpretation of the
encoding UML model should be close to the interpretation of the original architectural description so the model
is intelligible to both designers and UML-based tools. Also, resulting architectural descriptions in UML should
bring conceptual clarity to a system design, avoid visual clutter, and highlight key design details. All relevant
architectural features for the design should be represented in the UML model, keeping in mind that not all uses
of UML are supported equally by all UML tools, which can limit documentation options [5].
3.1 Documenting components

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There are two meaningful ways of representing architectural components in UML, by using UML
classes or UML components.A natural candidate for representing component types in UML is the class concept.
Classes describe the conceptual vocabulary of a system just as component types form the conceptual vocabulary
of architectural documentation. Also, UML classes, like component types in architectural descriptions, are first-
class entities and rich structures for capturing software abstractions.
Structural properties of architectural components can be represented as class attributes or associations,
behavior can be described using UML behavioral descriptions, and generalization can be used to relate a set of
component types. The type/instance relationship in architectural descriptions is a close match to the class/object
relationship in a UML model, although it's not identical. A component instance might refine the number of ports
specified by its type or associate an implementation in the form of an additional structure that is not part of its
type’s definition. This can be overcome by using subclasses, so that instance of a subclass represents instance of
a component.
On the other hand, UML components have an expressive power similar to that of classes and can be
used to represent architectural components as in the first strategy, with slightly different graphical notation. In
addition, component can own packagable elements along with elements a class can own, which can be useful in
some cases.
3.2 Documenting connectors
While the Connector element introduced in UML 2 is intended to represent communication links (a
good semantic match to architectural connectors), it lacks the expressiveness needed to satisfy our completeness
criteria. In particular, semantic information such as a connector’s behavior or interfaces cannot be associated
with a UML Connector. As a result, we examine other options available in UML 2 and how each compares to
our criteria. We restrict our-selves to solutions that avoid importance of the UML to assist communication
among varied documentation users, but briefly mention one simple specialization (examples of more complex
specializations include [7, 9]).
Even though there is connector concept in UML, it lacks fluency needed to be considered as a solution
for documenting architectural connectors, e.g. it lacks ability to associate semantic information with a connector
or to clearly document architectural connector roles. Therefore, three strategies for representing connectors in
UML will be considered:
 using UML associations
 using UML association classes using UML classes
Using UML associations for documenting connectors allows visual distinction between components
and connectors. Different types of connectors can be distinguished by labeling each association with a
stereotype (Figure 1).
This strategy lacks ability to express semantic information connectors provide, because roles of
connector can’t be defined by associations (since associations don’t have UML interfaces or ports), and
associations can’t own neither attributes nor behavioral descriptions. Nevertheless, this strategy is useful when
purpose of documentation is identifying where different types of connectors are used in a system.
FIGURE 1:- Documenting connector using link

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The second strategy consists of using UML association class for describing connectors (Figure 2). This
strategy allows semantic descriptions of connectors, by using attributes and behavioral descriptions of a class, as
well as creating substructure of connectors, if needed.
FIGURE 2:- Documenting connector using association class instance
Also, connector roles now can be represented as UML ports on the association class, which enables
same level of expressiveness that component ports have (Figure 3).
FIGURE 3:- Documenting connector using association class instance with ports
However, this brings out issue of attaching component ports to connector roles. This can be solved
either by role name being added to corresponding component port, or by using assembly connectors between
ports of objects representing the connector and the ports of the objects representing the components. First
solution doesn’t affect visual clarity, but it lacks standard tool support, and second solution introduces
substantial visual clutter.
The third strategy consists of using UML class for documenting connectors (Figure 4).
FIGURE 4:- Documenting connector using object
This strategy allows same expression capabilities as the previous one, but also resolves the component
and connector attachment problems by explicitly using UML assembly connectors, removing the potential
ambiguity of the second strategy. Unfortunately, this solution presents the poorest visual distinction between
components and connectors, especially if classes are used for documenting components. This problem can be
mitigated by using different UML concepts to represent components and connectors, as shown in Figure 5,

5
where UML components are used for representing architectural components, and class is used for representing
connector.
FIGURE 5: - Documenting connector using object, UML components document components
If the goal of documentation is to identify where different types of connectors are used in a system,
particularly if the connector types are well known and understood, first strategy is a good choice. This strategy
is a good choice for “first drafts”, in which specific connector semantics have not been defined, but rough
choices should be identified by name. Drawback of this strategy is its inability to describe semantics and role of
a connector. Second strategy is a good choice when connector semantics need to be described, but specific
component port and connector role attachments are not important. If these attachments are important, third
strategy can be used. An Association, like a Connector or class connector, is a poor solution in terms of
completeness. Because this type of stereotype require the graphical support which is not offered by the UML
tools.
4. CONCLUSION
In previous versions, the UML has been an out of depth for documenting software architectures.
Though architectural concepts could be represented using different UML modeling elements, in many cases
there has been no clear best option for documenting some concepts, often resulting in compromising
completeness or semantic match to fit within the UML vocabulary.
UML 2 is well defined tools for describing components and connectors from its predecessors. It has
improved considerably by adding new things such as Structured Classifier and Port, which are excellent
semantic matches to their corresponding architectural concepts. These improvements provide a clear best
option, and reduce the confusion that can be caused by modeling the same architectural concepts differently for
different systems or in different organizations.
However, there has not been a similar bound forward in terms of documenting architectural connectors.
The new UML 2 Connector modeling element is not satisfactorily rich, making it difficult to associate detailed
semantic descriptions or representations with them; consequently, they are a poor choice for
representingcomponents and connectors.Also, concept of a part, introduced with composite structure diagrams
in UML 2 can be taken into thought when showing complex properties of the containing structured classifier.
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