Conditional Execution - A Pattern for the Implementation of Fine-Grained Variabilities in Software Product Lines

Conditional Execution: A Pattern for the Implementation of
Fine-Grained Variabilities in Software Product Lines
Jadson Santos1,2, Gleydson Lima1,2, Uirá Kulesza1
Demóstenes Sena1, Felipe Pinto1, Jalerson Lima1
Alexandre Vianna1, David Pereira2, Victor Fernandes2
1
Department of Informatics and Applied Mathematics (DIMAP) – Federal University of
Rio Grande do Norte (UFRN) – Natal – RN – Brazil
2
Informatic Superintendence (SINFO) – Federal University of Rio Grande do Norte
(UFRN) – Natal – RN – Brazil
jadson@info.ufrn.br, gleydson@info.ufrn.br, uira@dimap.ufrn.br,
demostenes.sena@ifrn.edu.br, felipe.pinto@ifrn.edu.br,
jalerson.lima@ifrn.edu.br, strapacao@gmail.com, david@info.ufrn.br,
victorhcf@gmail.com

Abstract. This paper presents the Conditional Execution design pattern that
aims to help the implementation of fine-grained variabilities in the context of
software product lines of information systems. The pattern has been used
successfully in three product lines of web information systems developed by
Informatic Superintendence (SINFO) at Federal University of Rio Grande do
Norte.

1. Intention
The Conditional Execution design pattern contributes to the implementation of
fine-grained variabilities in the context of software product lines (SPL) [Clements and
Northrop 2001] [Czarnecki and Eisenecker 2000] [Weiss 1999] of information systems.
It provides support to the modularization of a certain variability located in one or more
modules to values assigned to configurations parameters, allowing its activation (or
deactivation) dynamically in the system.

2. Example
In order to illustrate the need for the usage of the pattern, we present examples
from a Library Management module of a software product line of an academic
information system. We use the punishment functionality for users who return late
borrowed books. This functionality defines a variability that determines the kinds of
punishment, which can be: (i) a payment in cash or (ii) a suspension for a period of time
without to make new loans.
During the execution of the system, which represents a product (instance) of the
SPL, the decision for execution of such punishment variability can happen several
times, for example, during the execution of a new loan, returning a book or printing a
bill for payment. The variability code is also spread among the system layers, from the
calculation of the amounts of punishment in the business layer to the user visualization
of loan functionalities in GUI layer. In some cases, the system manager can provide a

“period of forgiving” during which the users do not receive punishment, even if they
return the material overdue. All variabilities related to the punishment feature must be
deactivated from the system and then being re-activated immediately after the system
manager request.
Listing 1 shows the code of the ReturnLoanProcessor class from business
layer containing the functionality “return of a book loan” without the punishment
variability. We want to create a variation point inside the core conditional statement that
verifies if the return of the book is delayed. It is noticed that the code that creates a
suspension is intertwined with business code that verifies the permission of the operator
(library employee who performs the loan), updating the data to commit the loan and
sending e-mail information to the user about the book return.

Listing 1: Example of fine-grained variability in business layer

Software product lines of medium and large scale with a large number of
features, tend to have fine-grained variabilities [Kästner, Apel and Kuhlemann 2008]
that are intertwined with the implementations of other common and variable features.
It is necessary to implement the variability of execution the punishment feature
in the example in Listing 1 in a way that, depending on the type of punishment that is
currently active, the code that implements such variability is executed, creating the
correct punishment for the user, instead always create a suspension.
The decision for the execution of the variability need be codified to allow its
dynamic change, reflecting if the punishment variability is currently active or not. In
addition, it is also need the introduction of the variability implementation inside of
classes of the business layer. In Listing 1, for example, the punishment variability must
be implemented using another conditional statement (“if”) that determines its execution.

Finally, another requirement is that the proposed solution to implement the
punishment variability can be used in other modules of the system, eventually
implemented using other technologies. Listing 2 shows, for example, a Java Server
Faces (JSF) web page from the same system, which implements a menu with the user
options related to the functionalities of the book loan. The item "Print Bill for Pay
Library Fines" should be visible to users only if the variability of fine is enabled.

Listing 2: Example of fine-grained variability in view layer.

Object-oriented (OO) solutions such as design patterns [Gamma et al 1995] can
contribute to the modularization of SPL variabilities in information systems by
providing flexible structures to implement optional and alternatives features, which may
be activated depending on the desired behavior in the product. For example, the State or
Strategy [Gamma et al 1995] design patterns can be used to implement alternative
variabilities, such as the example shown in Listing 1, which involves choosing one
among a set of algorithms or possible states.
Although the adoption of traditional design patterns can help the modularization
of SPL variabilities in information systems, the decision to instantiate or execute such
variability may depend on many other parameters configured from the SPL domain.
These parameters can be available during the process of derivation of the product
(configuration parameters of the product) or only during its execution.
There are other modularization techniques that can be used in the
implementation of fine-grained variability of information systems, such as aspect-
oriented programming and conditional compilation. Each one of them faces difficulties
when used in this context. Aspect-oriented programming (AOP) enables the
modularization of such variabilities. However, the implementation of fine-grained
variabilities is usually strongly coupled with the business code where it is located.
Because of that, the use of aspects requires to expose all parameters used by the
variability, which demands the codification of complex pointcuts [Kästner, Apel and
Kuhlemann 2008]. Furthermore, in the context of the development of information

systems in the industry, it is not common to find software engineers who have advanced
knowledge for using such technique.
The Conditional Compilation is another technique that can be used for
implementing fine-grained variabilities. This technique works by defining a set of pre-
processor directives in the source code, which indicate the inclusion of a fragment of
code on the product of a SPL. However, this technique provides a series of limitations
compared to other existing ones: (i) it is possible to define only boolean parameters
when specifying the variability, and (ii) all the variabilities need to be addressed and
solved during the compilation of the system, there is no support for the definition of
variabilities, whose execution can be decided during the system execution.
3. Context
Nowadays there is a great demand in the industry for the customization of
information software systems already developed for a given institution, in order to adapt
those systems to be used in environments from other institutions. One of the motivations
for such scenario is to increase productivity and quality of development of new
information systems through the reuse of design and code of previously developed
systems.
In this context, software engineering approaches to the development of software
product lines (SPL) emerge as a promising proposal. A SPL can be seen as a family of
systems that maintains: (i) a set of common features for all members of the family,
known as similarities; and (ii) a set of variable features that changes based on specific
needs of a SPL family member (product), called variabilities. A feature represents a
functionality or property of SPLs that is used to capture their similarities and distinguish
their variabilities.
The development process of SPLs involves not only the identification and
modeling of their similarities and variabilities, but also the definition of a flexible
architecture and the choice of adequate implementation techniques to modularize the
SPL variabilities.
.
4. Problem
The Conditional Execution pattern proposes to address the following question:
How to implement fine-grained variabilities in information system product lines in order
to allow dynamic product configuration, without causing major changes impacts on
architecture designed, keeping the performance expected by the system and being
flexible enough to be implemented by all its modules and/or layers?
The following forces emerge from this problem:
(1) Dynamic Configuration: The variability choice should be performed
dynamically, thus giving more flexibility to the SPL customization.
(2) Low Impact: The implementation of the variability should not require
substantial changes on the SPL structure .
(3) Fine Granularity and Crosscutting: The variability can appear in any layer or
piece of code, being fine-grained and/or crosscutting.

(4) Performance: The solution should run with low overhead for the system.

5. Solution
The pattern proposes to map each identified variability to a configuration
parameter, which allows defining if the variation will be performed at runtime according
to the parameter value.
The parameters are stored in a persistent repository, which allows easily reading
and updating their values. A component is concerned in retrieving the parameter values
in a transparent and efficient way, so it can instantiate the variability code to be executed
based on these values.
The proposed solution is a combination of conditional statements "ifs" with
configuration parameters of the system. Thus, it can decide which variability will be
present in a particular product by adding or removing variabilities at runtime without
keeping this decision hardcoded.

6. Structure
The Conditional Execution pattern consists of four main participants, which are
illustrated in Figure 1:

Figure 1: Conditional Execution pattern structure.

6.1 Target Classes
It represents the system components where variabilities happen. The execution
of the variability code depends on the configuration of the system parameters values. In
the context of web information systems, Target Classes may be in any layer of the
application, includying dynamic HTML content pages.

6.2 Variability Implementation

The code that modularizes the variability is located within the Target Classes. It
usually consists on: (i) a direct implementation of variability code inside a Target Class;
or (ii) a call to a component that implements the variability. The execution of this
snippet is decided by the Execution Manager.

6.3 Execution Manager
The Execution Manager is the central element of the pattern. It determines if
certain SPL variability will be executed or not based on configuration parameters from
the system. The main tasks of this element are: (i) to get the parameters values from the
repository as efficiently and transparently as possible; and (ii) to determine the
execution of the variabilities associated with the retrieved parameters on Target Classes.
Execution Manager contains the decision logic to determine if the variability is
performed, removing this responsibility from the Target Classes. It provides access to
configuration parameters, allowing the runtime adaptation of the variability. Finally, the
Execution Manager must also provide mechanisms to optimize and minimize access to
the repository, and it must maintain the parameters values synchronized with the values
stored in the repository.

6.4 Parameters Repository
The Parameters Repository is responsible to store the parameters values used
during the conditional execution. It allows storing and updating the parameters values
during the application execution. It is fundamental that the retrieving of the parameter
values is not costly for the system performance. Database systems or local files are
examples of technologies that can be used as a parameter repository.

7. Dynamic
The following scenario defines the behavior of the Conditional Execution
pattern during the runtime execution of variabilities.

Scenario 1: Variability Execution
An instance of the Target Class calls the Execution Manager to determine if the
variability will be performed. The Execution Manager retrieves the parameter value by
calling the Parameters Repository. After that, the Execution Manager indicates to the
Target Class if the Variability Implementation must be executed or not. Figure 2 shows
a sequence diagram that illustrates this scenario.

Figure 2: Dynamic of the Conditional Execution pattern.

8. Consequences

The Conditional Execution pattern brings the following benefits:

• Simplicity. It simplifies the implementation and customization of fine-grained
variabilities by allowing the extraction or introduction of SPL variabilities in
existing legacy information systems.
• Load-time or runtime customization. Variabilities can be configured at load or
execution time. Changes in the system business rules, for example, that demands
the addition or removal of variabilities may be performed by the software
engineers without the need to recompile the system, such as using techniques
like Conditional Compilation.
• Preventing compilations issues. All variabilities code are present in the SPL
products, the pattern eliminates the possibility of generating compilation errors
during the product derivation process compared to the Conditional Compilation
technique [Kästner and Apel 2009].
• Reducing code complexity. It avoids the implementation of aspects with complex
pointcuts that need exposing several parameters. It allows introducing variability
code based on parameter values that can be easily implementing in any
mainstream programming languages.

On the other hand, Conditional Execution pattern has the following drawbacks:

• Poor variability modularization. When compared to other techniques such as
aspect-oriented programming, the Conditional Execution pattern does not
provide an adequate modularization, because it does not promote the separated
and localized implementation of fine-grained variability. However, the usage and
adaptation of virtual separation of concerns (VSoC) tools [Kästner, Apel and
Kuhlemann 2008] can help to overcome this deficiency.
• Late detection of variability correct configuration. Because the Conditional
Execution pattern is an implementation technique that enables the runtime
decision for the execution of SPL variabilities, the effective test to verify the
correct configuration of the system with their respective variabilities can be done
just at load time and/or during the system execution.
• Exposure of full product line code. The code of all variabilities is always present
in every SPL product, requiring only changes in parameters values for activating
each of these variabilities. This may not be suitable for some business models, in
which the product price depends on the amount and kind of variabilities enabled.

9. Known Uses
In recent years, the Conditional Execution design pattern has been used to
implement different types of fine-grained variabilities in the information systems of the
Informatics Superintendence (SINFO) at the Federal University of Rio Grande do Norte
(UFRN) [SINFO / UFRN 2012 ] [GIS / SINFO 2012], such as:
• SIPAC - Sistema Integrado de Patrimônio, Gestão e Contratos: It provides
fundamental operations for the management of the units responsible for
finance, property and UFRN contracts, therefore, acting through activities
“middle” of this institution. The SIPAC fully integrates administrative area
since the request (material, service, supply of funds, daily tickets, lodging,
informational material, maintenance of infrastructure) until internal
distributed budget controls.
Among the several features of SIPAC using this pattern, we can cite:
o Lock Materials Purchase: It indicates whether the system will block
the request of materials if the available balance is exceeded.
o Editing the Contract Occurrences: If the system possesses the
operation to change/delete occurrences of contracts.
o Indication Request Period for Scholarships: The period in which the
operation of request for financial aid for students is enabled.

• SIGRH - Sistema Integrado de Gestão e Recursos Humanos: It automates the
human resources procedures, such as marking / changing vacation, retire
calculations, functional assessment, sizing workforce, frequency control,
trainings, online services and applications and functional registers, personal
department reports, among others. Most operations have some level of

interaction with the nationwide system SIAPE (Sistema Integrado de
Administração de Recursos Humanos), while others are only local services.
Among the several features of SIGRH using this pattern we can cite:

o The Training Server: It sets minimum grades and work hours that an
employee must reaches to pass in a training course.
o Chief/Vice-Chief Lock Vacations: It sets whether the chief and the
vice-chief of a unit can enjoy the vacations in the same period.
o Validation of the Employee Vacations: It defines if the validation
rules at the moment of creating a vacation will be applied or not when
the manager of the Personal Department creates the vacations for an
employee.

• SIGAA - Sistema de Gestão de Atividades Acadêmicas: It automates the
procedures in academic area through the modules: undergraduate,
postgraduate (stricto sensu and lato sensu), elementary school, high school
and technical school; submission and projects control and scholarship
research, submission and extension actions control, submission and control
of projects education (monitoring and innovations), library management
system, reporting of academic professors productions, teaching activities and
virtual distance learning environment called “Virtual Class”. It also provides
specific portals for: rectory, teachers, students, tutors distance learning,
coordination (stricto sensu, lato sensu and undergraduate), and evaluation
committees (institutional and faculty).
Among the several features of SIGAA using this pattern we can cite:
o The Online Enroll: It sets whether students complete enrollment by
the system or in person way only.
o Calculation of Academic Performance Indices: It calculates the
indices that assess the academic performance of students in
accordance with the strategies that are configured by the pattern.
o Method Evaluation of students: If students will be evaluated by
grade, aptitude or concept.
o Punishment for the Delay in the Library: If users suffer fine or
suspension for delaying loans of books in the library.

The mechanism of user authentication is another feature that uses the pattern, it
is present in all three systems mentioned above, which can use a database or network
authentication with LDAP.
Since one of the characteristics of the pattern is its simplicity of implementation,
it can be applied easily in information systems. An example of these systems can be the

ERPs systems (software integrated enterprise resource planning). These softwares have
features for presenting a large amount of variability because they are designed to be
deployed in as many customers as possible and each of these customers have a business
processes whose variability must be answered.

10. Implementation
This section presents an example of how the Conditional Execution pattern can
be implemented. This example is the same shown in Section 2 about the punishment
variability for the overdue materials (books, journals, proceedings, among others) from
Library Management module. During the discussion of the example is highlighted how
the forces involved with the pattern were implemented.

1º Step: Identifying the Target Classes
Inside the SPL SIGAA, there are two variabilities related to the user punishment
functionality: (a) cash fines for each day of delay in return of the material, and (b)
suspend the user for a certain amount of days, during which the user cannot do new
loans.
The using of the punishments functionality is related mainly with two scenarios
of implementation in Library Management module: (i) the execution of a new loan when
the system must not allow punished users get a new loans and (ii) at the moment of
material return when the system must verify if it has been returned late and then it
generates a punishment for the user. These two actions are performed in SPL SIGAA
respectively by business classes LoanProcessor and ReturnLoanProcessor, which are
characterized as Target Classes of the patterns. Both classes are part of the business
layer of the SPL SIGAA which is organized following the tier architectural pattern
[Buschmann et al 1996].
Inside the functionality user punishment, there is another action that involves
print bill for pay library fines. This action should be only enabled if the variability "fine"
is properly configured. Inside the SPL SIGAA, the places where this variability happens,
which are characterized as Targets Classes are: (i) the Managed Bean
PrintBillPayLibraryFinesMBean, and (ii) the following JSP pages: student_menu.jsp,
professor_menu.jsp and server_menu.jsp.

2º Step: Mapping each identified variability to configurations parameters
After identification of Targets Classes, you need to create the parameters
corresponding to punishment variability. For this case, there are two punishment
variabilities. Thus, two parameters were defined:
• SYSTEM_WORKS_WITH_SUSPENSION

• SYSTEM_WORKS_WITH_FINE

The parameters are declared in a Java interface called LibraryParameters, which
is shown in Listing 3. This interface is used by Targets Classes and Execution Manager
to reference the parameters via Java source code. Each parameter has an identifier.
These identifiers are created sequentially, so they are unique for the entire SPL.

Listing 3: Interface with parameters declarations.

After that, we need to persist parameters in the Parameters Repository. In the
specific case of SPL SIGAA is used the technology of the database to persist
parameters. It facilitates create, access and change parameter values. Thus, the creation
of parameters is inserting them into the database. Listing 4 shows the creation of the
SYSTEM_WORKS_WITH_FINE parameter in the database. Besides the identifier and
the parameter value, other information such as a brief description and identification of
the module of the SPL SIGAA that the parameter belongs are persisted, to facilitate its
use through the system.

INSERT INTO comum.parameter (name, description, value, id_subsystem,
id_system, identifier)
VALUES ('SYSTEM_WORKS_WITH_FINE',
'Define if the system will use fine like punishment', 'true', 14000,
2, '2_14000_8');
Listing 4: Parameters creation in repository

The extra information above referred is not essential to the operation of the
pattern. It is not the purpose of the pattern to define of persistence techniques that have
to be used, other techniques can be tried to implement the Parameters Repository.
The product derivation can be done by changing the parameter value in the
database, as shown in Listing 5. An interesting strategy is creating an use case for
system parameters management in order to pass the responsibility to choose which
variability will be presented in a particular product for some system manager.

UPDATE comum.parameter set value = 'false' where identifier =
'2_14000_8';

Listing 5: Making product derivation using Conditional Execution pattern.

Thus, simply changing a value in the database determines the pattern
characteristic of dynamic configuration.

3º Step: Implementing the Execution Manager
The Execution Manager is the main component in the implementation of this
pattern. It contains a logical decision whether a particular variability will be performed
or not.
Listing 6 shows a possible implementation of the Execution Manager. In this
implementation a method checks if a given parameter variability happens retrieving the
parameter from repository and returning its boolean value. If the parameter value is true,
the variability is present in the product line and must be executed, if the value is false,
the variability must be not executed.

Listing 6: The Execution Manager

Normally, due to the use of this pattern, there is a considerable amount of access
to the configuration parameters that can affect the system performance. The large
number of data accesses to the Parameters Repository is because the system during its
execution has to check in all places where variability may happen (variations points) if
the variability is present in that particular product or not. Even if changes in a specific
variability present in a product are rare, this checking is always necessary.
For this reason, it is recommended to adopt a strategy to minimize the number of
accesses to the Parameters Repository. This strategy can be implemented in various
ways. It is not the objective of the pattern to define a specific implementation strategy to
achieve this aim.
How in this example of implementation we used a database system, to minimize
the impact on system performance it was implemented a cache strategy. This
implementation maintains information about the last time that the value of each
parameter was synchronized with the value of the repository. When timeout is reached,
the Execution Manager reloads the parameter value. This strategy is implemented by the
method getParameter in Listing 6.
If you followed this strategy of cache, the Execution Manager should also keep
an operation that forces a reload of a parameter or set of parameters whenever requested.
This is useful when the value of a parameter is changed and this change should be
immediately reflected in the behavior of the system.
The caching strategy used by Execution Manager ensures low impact on system
performance, reducing queries to the repository, one of the forces that the proposed
pattern undertakes to deliver.
This third step of the pattern implementation needs to be done once. This
implementation can usually stay in the SPL architecture and it be used by all variability.

4o Step: Defining the Variability Implementation
The next step is to implement the specific code for each system variability. This
code will be called by the Execution Manager if the variability happens in the product.
Listing 7 shows a simplified code snippet of fine variability implementation in SIGAA
SPL.

Listing 7: Fine variability implementation.

5º Step: Calling Conditional Execution from Targets Classes
A conditional execution is implemented to generate the punishment for the
material delay return depending on which of variability is currently enabled. Listing 8
shows the business class code ReturnLoanProcessor that is responsible to implement
such functionality with the introduction of variability. To have a clear perception of this
pattern, we can compare the code in Listing 8 with the code shown in Listing 1, which is
presented in the same business class without using the Conditional Execution pattern.

Listing 8: Example of Conditional Execution in business layer
We can see in the code in Listing 8 that the implementation was carried out with
a low impact, since no change was needed in the core of SPL. Besides, the call to
Execution Manager is a simple implementation of the method invocation and it can be
perfectly included at the point where the dynamic derivation should occur.
Another variability related to the delay of the loan is SIGAA SPL variability
“Print Bill for Pay Library Fines”. This functionality should be performed only if the
variability “fine” is active in the system. In this case, a link is shown to the user
allowing the printing of payment bill. This is also a typical example of conditional
execution of fine-grained variability that can be implemented using the pattern. Listing 9
shows a snippet of a webpage of LPS SIGAA, which includes a link to print the bill
only if the variability “fine” is active. Moreover, it is also presented the code snippet of
class PrintBillPayLibraryFinesMBean that is responsible for accessing the Execution
Manager to verify the occurrence of variability in the product.

Listing 9: Example of Conditional Execution in view layer.

11. Variants
The Conditional Execution pattern can be used in a way that it performs more
complex decisions than just boolean decisions that verify if a variability will be present
or not in a product. This section describes two variant implementations of the pattern
that are being using by SINFO/UFRN.
To illustrate the first approach, consider the functionality that checks the timeout
between loans in the Library System modulo of SPL SIGAA. For this functionality there
is an integer value that defines the minimum time, in hours, that a user can make a new
loan of the same material. Besides, it makes possible to determine a minimum time
between different loans for each product, this verification can be disabled in some
products. Listing 10 shows the code of the Target Class where occurs this verification.

Listing 10: Conditional Execution of Integer Variability

Instead of using a boolean parameter to determine if the variability should occur,
it was created only one parameter of type integer. If this parameter value is greater than
zero, the Execution Manager enables the execution of verification. At the same time, the
parameter value is also used to calculate if the minimum time between loans was
obeyed, throwing an exception if the business rule is not followed. Listing 11 shows an
alternative implementation of the Execution Manager that verifies if a variation of type
integer occurs, besides the method that returns this integer value to be used by the
variability.

Listing 11: Execution Manager for Integer Variabilities.

To this alternative implementation was added the information “type” to the
parameter, beyond the information previously shown in Listing 4. This information
allows determine how the variability should be treated. We call the variabilities that use
an integer type parameter of “Integer Variabilities”. We emphasize that this was a
solution adopted and it is not the goal of the pattern determines how these
implementation details must be performed.
The second approach is based on removing of the dependency that the Targets
Classes have with the Variability Implementation. In this approach, the Execution
Manager doesn’t just determine whether a Variability Implementation will be

performance in a Target Class, but it instantiates and returns to the Target Class the
Variability Implementation to be executed.
The solution adopted for this second approach makes use of the Strategy design
pattern [Gamma et al 1995]. Some strategies are defined. The names of the classes that
implement these strategies are mapping for parameters. If the variability is presented in
the product, the Execution Manager instantiates the concrete strategies contained in
those parameters.
For this approach was created a new type of parameter called “Strategy
Parameter”. This kind of parameter doesn’t contain a boolean or integer value, but a
class name that implements the strategy. The variabilities that use this kind of parameter
we call of “Strategy Variabilities”. Figure 3 outlines the structure for this second
approach. The functionality used is the same of Listings 1 and 8, the punishment of
users for Library Management module of SPL SIGAA.

Figure 3: Example of Strategy Variability implementation using Conditional
Execution pattern.

In this approach the method getVariabilityStrategies of Execution Manager
receives a map of parameters. The map keys are boolean parameters which determine
whether the variabilities happen and the map values are strategy parameters containing
concrete strategies to be instantiated. Listing 12 contains the code for a possible
implementation of the method getVariabilityStrategies.

Listing 12: Example of Execution Manager for Strategy Variability
If the variability contained in the map key occur, the Execution Manager
instantiates the strategy contained in the map value, returning to the Target Class a list
of strategies that should be executed in the product and performing the product
derivation at runtime.
Listing 13 shows the implementation of the same variability shown in Listing 8,
but now using the approach of strategy variability modularizing to treat the
functionalities “fine” and “suspension”.

Listing 13: Target Class using Conditional Execution for a Strategy Variability.

In this context, to add a new variability to SPL is necessary to create a new
strategy punishment that “extends” the class UserPenaltyStrategy. It must insert the new
parameters to the variability in Parameters Repository and add them to the map passed
as a parameter to the method getVariabilityStrategies of the Execution Manager. Thus,
a new strategy is instantiated by the Execution Manager and returned to be performed
without the need to add a new conditional statement in the Target Class always that a
new variation is added to the product line.
Listing 14 shows an example of information about three kinds of parameters that
can be used to implement this pattern.

-- boolean parameter --
INSERT INTO comum.parameter (identifier, name, value, id_system,
id_subsystem, type )
VALUES ('2_14000_8', ' SYSTEM_WORKS_WITH_FINE', 'true', 2, 14000, 1);

-- integer parameter --
id_subsystem, type)
VALUES ('2_14000_10', 'MINIMUM_TIME_BETWEEN_LOANS', '24', 2, 14000,
2);

-- strategy parameter --
id_subsystem, type)
VALUES ('2_14000_20', ' CLASS_NAME_SUSPENTION_STRATEGY',
'br.ufrn.sigaa.circulacao.negocio.SuspensionDefaultStrategy', 2,
14000, 3);

Listing 14: Example of three kinds of parameters used by the suggested
implementation of the pattern.

Other variants to the pattern implementation can be created, it depends if will
appear other variabilities which behave differently from those ones described in this
paper.

Acknowledgements
We are grateful to Professor Dr. Eduardo Guerra for his valuable suggestions
during the shepherding process that contributed to a broader understanding of the
proposed pattern. We also thank all the suggestions given by the participants of the
Writers' Workshop of SugarLoafPLop'2012.

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