Heavy-Weight and Light-weight UML Modelling Extensions of Aspect-Orientation in the Early Stage of Software Development
Aws A. Magableh,
Norazean Mohd Ali
Aspect-Orientation and Object-Orientation complement each
other in a number of aspects. Hence, it is imperative to investigate level of
adopting Unified Modelling Language (UML) by the Aspect-Orientation. This study
employed a systematic literature review to examine the approaches of Aspect-Oriented
UML (AOUML). The rapid growth of complexities of systems, of late have eventually
paved way for the emergence of new concerns. In fact these new concerns have
cut-cross other concerns and core classes in the system by their nature. Therefore,
it is crucial to focus on the concept of crosscutting concerns (Aspect), throughout
the whole development life cycle, as they are accountable for generating, disseminating
and interweaving depictions. The scope of this study is to depict and examine
the current state of art of Aspect-Orientation modelling using UML. The UML
diagrams have been implemented on the top of Object-Orientation concepts, it
has not been meant to be used to model Aspect-Orientation. Thus, the motivation
of this study is to propose a complete tailored formwork that represents Aspects
constructs using all UML diagrams based on AspectJ constructs. The objective
of this present study is find out the shortenings, lack of support, advantage
and disadvantage of the existing well-known approaches of Aspect Modelling based
on a carefully selected, evaluation and compression criteria. The examination
and analysis have revealed that there are some deficiencies of Aspect representation
in the early stage of software development, while using the existing UML. We
have concluded that extensive research has to be carried out, for us to get
a complete comprehensive framework modelling approach that covers all UML diagrams,
rather than just a few, moreover we suggest that the assumption of modelling
extensions have to depend on a reliable base.
Received: July 14, 2012;
Accepted: October 15, 2012;
Published: December 03, 2012
Software reusability is a portion of code that can be reused with other systems
with minor or no modification. This indicates building a system, by integrating
existing pre-engineered components. Reusable modules and classes reduce implementation
time board (Zakaria et al., 2002). OO (Object-Orientation)
promised to improve the software reusability by using different kind of techniques
such as inheritance and polymorphism. Inability of the OO paradigm to address
the entire separation of concerns concept is one of the reasons that reduce
software reuse in OO (Zakaria et al., 2002).
In the object-orientation programming concepts, systems are expressed as a collection
of incorporated classes and classs instance (objects). However, usually
the complex system and sub systems have some features that naturally cut cross
other classes, components or modules (core classes) which lead accumulatively
to increase the level of dependencies among these elements, when the dependencies
are high, the reusability is low. Thus, in the OO, these crosscutting components
(Aspects) are not represented in objects. All these are leading to have the
aspect-orientation concepts on board (Zakaria et al.,
Aspect-Orientation (AO) is not considered as a replacement for Object-Orientation
(OO), moreover, AO concept is mainly focused on Aspect-Orientated Programming
(AOP), with less attention paid to the early stage of Aspect-Oriented Software
Development (AOSD) such as, design and modelling (Laddad,
AOP allows programmers to implement the concept of separation of concerns which
is so important once it comes to software development processes (Magableh
and Kasirun, 2007). Also, AOP overcomes the problem of code spreading over
the core concerns, which is called as Code Tangling and Code Scattering. Nevertheless,
OO is incapable of efficiently solving this issue, when it implements the crosscutting
concerns. Additionally, AOP solves these issues by implementing new modularity
unit called as Aspect. The AOP has achieved a very considerable growth in the
industrial environment and academic researches, which has led to an interest
in AO techniques for all software life cycle stages (Przybylek,
Due to the importance and usability of AOP, it has been extended to cover the
rest of software development stages. In fact, currently there are many AOM approaches,
however, the most well-known and established approaches are those capable of
handling aspect modelling using UML, because UML is the most popularly used
modelling language tool in the industry (Ali et al.,
2007). However, there is a lack of uniform standards. With the current state,
UML is not capable of representing properties of AO constructs and the crosscutting
nature of the aspects, at the design level (Grundy, 2000).
UML modelling extension mechanisms have been categorized into two types. The
first one is the UML Meta Object Facility Metamodel (Heavy-weight) and the second
one is the Constructing UML Profile (light-weight). The UML Meta Object Facility
Metamodel (MOF metamodel) is referred as heavy-weight extension. The metamodel
constructed can be as communicative as needed (Rui et
al., 2009). Constructing the MOF metamodel is harder than constructing
a UML profile and does not have enough supporting tool as compared with UML
profile. Whereas, the second type UML Profile (light-weight) is usually called
as light-weight extension because all the existing UML profile extension construction
techniques do not implement any new UML Meta-model elements. Constructing UML
profile extension techniques are usually considered to be predefined set of
constraints, tagged values, graphical representations and stereotypes. Constructing
UML profile extension method supplements aspect based on the flexibility and
extendibility nature of the standard UML domain modelling (Przybylek,
The objective of this study is to provide a review on the current existing
Aspect-Oriented Modelling approaches using Unified Modelling Language. Moreover,
the study aims to provide some carefully selected evaluation and comparison
criteria to compare the approaches against, which shows the limitation of these
Aspect-Oriented Modelling approaches. Finally, this study is an eye-opening
on the improvement that could take place to enhance the existing Aspect-Oriented
Modelling Approaches such as taking all AspectJ constructs and all UML diagrams
EVALUATION AND COMPARISON CRITERIA
Here, the selected AOUML modelling approaches are compared and contrasted.
The core idea of this comparative analysis is to identify the gaps in the field
and to set the platform to address those gaps by answering the research questions.
This will enable us to unambiguously depict the approach to be employed for
assembling the criteria catalogue and to describe a general narrative schema.
The procedural rationalization, which follows the criteria design and assemblage,
offers an essential platform for executing an extensive analysis of existing
AOUML Modelling approaches. While performing the analysis we will make sure
that none of the measurable criteria are omitted. Furthermore, the more clearly
defined criteria and the apt measurement resources are not also excluded. We
have illustrated the apparent catalogues for these criteria; generally, the
comparison criteria should fulfil certain level of standardization and guidelines
(Shukur and Mohamed, 2008) as follows:
||Language specification (LS): This type depicts few
principles associated with the UML modelling languages. The UML Modelling
Language Version (UMLMLV) is used by a particular approach, which indicates
whether the approach uses latest version of UML or not, the UML edition
numbering is indicator of this factor. The Extension Mechanism (EM) articulates
the UML extension employed by a particular approach, precisely this factor
specifies whether the extension is Light-Weight (LW) or Heavy-Weight (HW)
and the indicators are either HW or LW. Diagram Type (DT) identifies the
UML diagrams incorporated in the extension of a particular approach and
the name of the diagram is the indicator of this factor
||AspectJ constructs/syntax (AJC): This is a very significant criteria,
as far as this study is concerned, because we are going to investigate the
complete list of AspectJ constructs, which are widely used and well-recognized
in the AspectJ languages in the industry to execute reverse engineering
(button-up). This extensive study will enable us to escalate the reliability,
level of understanding and stable changeover from one stage to the other
(Kande et al., 2002). The criteria have been
inspired from Laddad (2002).The full or partial support
indicates the values of this factor
||Maturity issues (MI): This catalogue indicates the capabilities
of the selected UML Aspect modelling approaches. Even though there are a
lot of approaches available, this study has focused only the most popular
and recognized approaches, which have drawn the attention of scholars (Reddy
et al., 2006). This factor constitutes the maturity of the Modelling
Examples (ME), which is employed to exhibit the dependability of the proposed
modelling and the maturity of the Application in Real-World Projects (ARWP),
which illustrates the applicability of the approach in realistic world
||Tool support (TS): This category emphasizes a number of criteria,
which mainly focus on a tool support for the selected approaches. This catalogue
is further classified as Modelling Support (MS), Code Generation (CG) and
Model Kernel Extraction (MKE)
||Complete framework support (CFS): This factor highlights a composition
of other factors. We call an approach as a complete framework, if it captures
all the AspectJ constructs using all UML diagrams 2.4 (not only few) and
has a comprehensive tool support for auto AspectJ generation and model kernel
extraction in to text file such as Petal file
The Aspect-Oriented UML modelling approaches are bifurcated into as constructing
UML profile and UML Meta Model Extension. Principally, constructing UML profile
extension is called as light-weight extension. This is due to the fact that
all the existing constructing UML profile extension techniques, do not apply
any novel UML Meta-model elements. Furthermore, the constructing UML profile
extension techniques are generally recognized as a predefined set of limitations,
marked values, graphical representations and typecasts. Consequently, the constructing
UML profile extension technique enhances the aspect, depending on the adaptability
and extensibility of the standard UML domain modelling (Przybylek,
2010). The second category UML Meta Model Extension signifies the fundamental
rules and norms for constructing the domain conceptual models to the Meta Model.
The UML Meta Model Extension is recognized as model of a modelling language.
Furthermore this category is a heavy-weight extension, due to the capability
of proposing novel UML Meta models to signify the aspects and their crosscutting
nature (Rui et al., 2009). Few studies of AOUML
modelling have revealed that, there are a total of fourteen, matured and well-established
Implementation of software components using aspects: The Aspect-Oriented
Component Engineering (AOCE) is aimed at distinguishing an assortment of slices
or aspects from a system. A component is capable of providing services to other
components or will get the services form its counterpart. Fundamentally, the
aspects impact a lot of other components that are acknowledged by breakdown
processes, such as perseverance and allocation. Further more aspects are employed
by developers to illustrate various perceptions on the capabilities of components
during requirements engineering and design. The AOCE depicts the aspect and
its details. It offers a novel framework for the purpose of illustrating and
analyzing the potentials of component from different angles (Grundy,
A toolkit for weaving aspect-oriented UML design: UML All Purpose Transformer
(UMLAUT) toolkit is a different kind of tool used for the MOF mechanism. It
is an aspect oriented UML model employed for effortlessly constructing explicit
weavers for generating high-level comprehensive design models. The UMLAUT facilitates
the developers to program the weavers at of UML Meta mode level. It offers an
extendible and reusable general purpose operator for various applications with
definite needs. All the AO designs might be developed with an application specific
weaver that optimizes the weaving process confirmed by UMLAUT (Ho
et al., 2002).
An UML-based aspect-oriented design notation for aspectJ: This is light-weight
UML extensions intended to be a design notation for AspectJ. Basically it broadens
the current UML standard notations and proposes a novel AspectJ weaving process
(Stein et al., 2002).
Theme: An approach for aspect-oriented analysis and design: Theme/UML
is used to generate distinct design models for each theme that evokes
from the requirements phase later it summarizes the concerns, which signify
some kind of functionality in a system. The Theme/UML is recognized as a heavy-weight
extension of the UML metamodel version, due to its capability of augmenting
novel elements to the basic representation. Fundamentally, the Theme/UML will
not restrict the UML diagrams, which are used for modelling. On the other hand,
package and class diagrams are exclusively used for modelling structures, whereas
the sequence diagrams are employed for modelling behaviours (Clarke
and Baniassad, 2005).
Weaving with state charts: This is aimed at independently modelling
an aspect from a specific type of aspect-oriented programming language. Here
the structural dependencies are expressed by class diagrams. This approach also
signifies the machines model and the behavioural dependencies of concerns and
offers a directive to constantly enhance the modelling from class diagram to
a prototype (Elrad et al., 2005).
Aspect-oriented software development with use cases: The significance
of the use case driven software development method has been recognized by expanding
the UML 2.0 metamodel. The Aspect-Oriented Software Development with Use Cases
(AOSD/UC) constitutes an efficient process, which is capable of separating the
concerns from the entire software development life cycle. In case of the design
phase, the component diagrams are converted into class diagrams, while sequence
diagrams are employed to model the behavioural features. Furthermore, the AOSD/UC
models the concerns with the help of use case slices stereotype and lacks support
tools (Jacobson and Ng, 2005).
Aspect-oriented software development with JAVA aspect components: This
indicates a hybrid mechanism, where it amalgamates the UML profile extension
and the abilities of UML, to produce various domain models and UML Meta object
Facility model mechanism, by proposing new Meta object/notation. It proposes
a platform dependent JAVA Aspect Component (JAC). The JAC comprises novel UML
notations. It supports all the steps of Aspect-Orientation development, which
ranges from design, to deployment. This approach employs the UML profile mechanism
to design aspects by augmenting stereotypes to qualify classes implementing
aspects and non functional concerns (Pawlak et al.,
Directives for composing aspect-oriented design class models: Aspect-Oriented
class design model comprises a set of aspect models and a primary model. Each
aspect model depicts a attribute that crosscuts the essentials in the primary
model. The aspect and primary models are aimed at obtaining an incorporated
design view. It characterizes a composition method, which employs composition
algorithm and decree, where the former is used when the default composition
algorithm is known or likely to produce erroneous models. The prototype of this
approach facilitates the composition of default class diagram (Reddy
et al., 2006).
Presenting crosscutting structure with active models: This presents
crosscutting structure, which is generally carried out using two means such
as: (2) tree views, which enables the developers to manually combine information
across numerous views and (2) static structure diagrams, which might be probably
victimized by the intense graphical intricacy. An active model is an approach,
which addresses these issues by introducing the accurate crosscutting structure
at the appropriate time. The right information is determined through automatic
projection and abstraction operations that select elements and relationships
likely to be of interest and that abstract those elements and relationships
to control the diagram complexity when too many similar cases occur. The information
is presented at the right time through a combination of a user-driven expansion
operation that adds detail to the model and interaction features that show some
information only on demand by the user (Coelho and
Join point inference from behavioural specification to implement: This
presents a novel join point selection mechanism depending on the condition of
machine specifications. The interfaces of a system encompass the requirement
of the effects of method approved on the state of the module instance. This
requirement does not describe the potential aspects, but explicitly describes
the apparent behaviour of the module. We have illustrated the capability of
a smart join point selection mechanism to conclude points that might be located
deep inside the implementation of a module and to infer the particular pointcut
that is totally articulated in terms of its specification element. It enhances
the class diagram and the composite structure to obtain the static structure
of the system and employs the machine extension to signify the behaviours of
the system (Cottenier et al., 2007).
A concern architecture view for aspect-oriented software design: The
concern architecture model is employed to cluster aspect designs in the context
of software architecture. It offers an aspect-oriented perception while designing
software. This model can be also viewed in the context of aspect analysis for
analyzing the influences of the modifications or adaptabilities in concerns
to be addressed by aspects. It includes a number of novel stereotypes to model
aspects such as: <<Aspects>>,<<Concerns>>, <<Bind>>,
<<replace>> and <<Unify>> (Katara
and Katz, 2007).
Weaving multiple aspects in sequence diagrams: This has introduced an
Aspect-Oriented UML approach using the standard UML. However, it has not proposed
any new notation and has not used the ability of UML extension assuming to maintain
the standards. Furthermore, it is originally based on Message Sequence Charts
(MSC) a standardized scenario language and employs the UML 2.0 sequence diagram.
In fact, no extensions are added to the UML Sequence diagram; instead a simplified
Meta model for Sequence diagram has been designed, which complies with the original
UML Sequence diagram by converting model in the supplementary tool support (Klein
et al., 2007).
Extending the UML metamodel to provide support for crosscutting concerns:
It has presented an extension to the UML metamodel to unambiguously obtain the
crosscutting concerns. It introduces an autonomous means to any programming
language and cross platform. The newly produced metamodel can be represented
in standard XMI format, moreover it lacks own tool to illustrate the modelling;
however it employs the current CASE tools to read this XML format. This language-independent
aspectual description can facilitate model transformations that are significant
to software development and maintenance, such as forward engineering, reverse
engineering and reengineering (Sharafi et al., 2010).
Separation of crosscutting concerns at the design level: an extension to
the UML metamodel: Aspect-Oriented UML Modelling has proposed an extension
by instituting a novel package called as AoUML, which comprises elements that
signify the primary AO concepts such as: aspect, advice, pointcut, parent declaration,
introduction and crosscutting dependency. It has also proposed reuse elements
from the UML 2.1.2 infrastructure and superstructure specifications (Przybylek,
Table 1 depicts the analysis and the evaluation based on
this study selected criteria. It shows that none of the most used (surveyed)
approaches did use the latest UML editions 2.4 and it implicitly shows that
none of these have tried to improve the proposed approach to fit the latest
Table 1 gives an idea that some of these approaches depend
on the UML edibility to be extended to model different domain model (lightweight),
some more used new notations (heavyweight), some did not amend the standard
UML and tired to use it as is and this is what Klein proposed. Pawlak tried
to propose a use of both UML extensions.
Table 1 depicted that only few types of UML diagrams have
been used by either LW or HW extensions. Majority of the approaches focused
on proposing an extension to model aspects using class, sequence diagrams. Some
more tried to use communication, package and use case diagrams. It has been
concluded that none were focused on the whole UML diagrams as one framework
and none proposed a complete set of aspect modelling notation using all UML
Table 1 explains explicitly that some of the approaches are
using AspectJ as a baseline for modelling aspects. However, none of the approaches
proposed a complete modelling set for all AspectJ detailed constructs.
Table 1 addressed the maturity concerns of the approach.
Maturity has been measured by providing a modelling example and that example
being a useful application in the real life. As stated in Table
1, some of these approaches have used a modelling example to demonstrate
their proposition and some other have not done that. For those who have done
it, some approaches provided too easy and duplicated examples and some other
provided too complicated examples which makes it so hard to ready, understand
and make use of it.
|| Evaluation and comparison criteria of different studies
|AJC: AspectJ constructs, MI: Maturity issues, TS: Tool support,
UMLMLV: UML modelling language version, EM: Extension mechanism, DT: Diagram
type, AJC: AspectJ constructs, ME: Modelling examples, ARWP: Application
in real-world projects, MS: Modelling support, CG: Code generation, MKE:
Model kernel extraction, LW: Light-weight, LS: Language support, HW: Heavy-weight,
Y: Yes, N: No
Finally, Table 1 shows that majority of the approaches did
not propose their own modelling tool; they used already existing tools and plug-in.
That leads to lack of support for AspectJ code generation, modelling extraction
into XML format such as SVG.
After the analysis and brainstorming took place on the result of this study,
it has concluded that there some limitations which have to be addressed by the
future researches. This study has proved that none of the existing approaches
is based on the latest UML 2.4 edition. Additionally, it has been shown that
majority of the existing approaches are based on some UML diagrams to represent
and model Aspects and none of them have came out with a complete set of modelling
notations for all UML diagrams and some UML diagrams such as timing diagrams
have not been put on the table of the discussion yet. Finally all the approaches
have provided some partial support to model Aspects based on AspectJ detailed
constructs. This study has opened new venue for research to see the ability
to provide a complete Aspectual UML 2.4 modelling framework based on AspectJ
detailed programming constructs to maintain the constancy and tractability in
all Aspect-Oriented Software Development.
In this study, we had reviewed different Aspect-Oriented UML modelling approaches.
Additionally, perspectives of various authors had been elucidated and analysed.
Moreover, we had studied the UML extension mechanisms provided to model aspects
using UML. We had analyzed the surveyed approaches by selecting some common
and critical factors and had presented in a tabulated format for clear understanding
and readability. Each and every one of these selected approaches had been evaluated
based on this study analysis criterion. Finally, we had found out that UML with
its current state is unable to efficiently represent aspects, moreover, not
all approaches depends on Aspect-Oriented programming to model aspects, majority
of these approaches do not represent all aspect-oriented programming using all
UML diagrams rather they focus one class diagram, sequence and state diagrams,
which should not be enough to effectively represent constructs of the aspect
in the early stage of software development.
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