=Paper=
{{Paper
|id=Vol-1603/10000018
|storemode=property
|title=Enabling Compositional Deadlock Checking of Component Compositions with Partial Bindings
|pdfUrl=https://ceur-ws.org/Vol-1603/10000018.pdf
|volume=Vol-1603
|authors=Vanessa Stricker
|dblpUrl=https://dblp.org/rec/conf/caise/Stricker16
}}
==Enabling Compositional Deadlock Checking of Component Compositions with Partial Bindings==
https://ceur-ws.org/Vol-1603/10000018.pdf
Checking Deadlocks in Component Composition with
Partial Bindings using Variability Modeling
Vanessa Stricker
(Supervised by Prof. Dr. Klaus Pohl)
paluno – The Ruhr Institute for Software Technology, University of Duisburg-Essen,
Gerlingstr. 16, 45127 Essen, Germany
vanessa.stricker@paluno.uni-due.de
Abstract. A large number of compositional deadlock checking techniques have
been proposed in order to overcome the state-explosion-problem. These ap-
proaches require all components in a composition to be fully bound. This re-
striction conflicts with the underlying reusability paradigm of component-based
software engineering, which often requires only parts of components to be re-
used and allows component compositions to be realized by a large set of similar
component configurations. Accordingly, compositional deadlock checking ap-
proaches are not applicable to component compositions, which can be realized
with partial bindings. We propose to overcome this problem by i) restricting the
number of realizations, which have to be verified and ii) removing behavior that
is not executed due to partial bindings.
1 Introduction
Component-based software engineering (CBSE) is a well-established paradigm in
information system development (especially for distributed information systems),
which advocates the reuse of components in order to build a set of large and complex
systems from existing components [21]. However, ensuring that components compo-
sitions are deadlock free is challenging. Deadlocks are a common source of errors in
systems of concurrent processes as they are common in component-based systems
[10] because components usually make implicit assumptions about the behavior of
their environment. When connecting components, their interaction might give rise to
unexpected deviations and inconsistencies w.r.t. the intended behavior of the system.
Early verification approaches, like deadlock checking techniques, which are based on
the specification of components, have become an important tool in CBSE in order to
detect errors in the interaction of components. Unfortunately, deadlock checking of
component compositions is subject to the state-explosion-problem, as the concurrent
nature of component-based system requires the computation of the global behavior. A
large number of compositional deadlock checking techniques have been proposed in
CBSE in order to address this challenge. Semmelrock and Majster-Cederbaum [20]
were able to prove that compositional deadlock checking is within PSPACE for acy-
clic component topologies.
1.1 Compositional Deadlock Checking Approaches
Compositional verification generally allows breaking down a verification problem
into smaller problems. Under certain conditions, a global property is proven by de-
duction from local properties of the components in a composition (cf. [4]). Composi-
tional deadlock checking approaches usually concludes the global deadlock freedom
of a composition from the local deadlock-freedom of its components. The conditions
of most compositional verification approaches require very restrictive composition
principles to allow analyzing the smaller verification problems independently from
each other. In the case of compositional deadlock checking approaches, these restric-
tive assumptions require all components to be fully bound, i.e. not to have any partial-
ly (cf. for example [1,12]) or unbound ports (c.f. for example [11]).
Two components are bound if there exists a connection between their ports. The
components can interact via those connections. If a component has partially bound
ports, the interaction of these components within a composition cannot include the
unbound functionalities. Thus, the execution of a component within a specific compo-
sition might only comprise a subset of the full behavior that has been specified for this
component. However, as compositional deadlock checking approaches only analyze
small parts of the component’s behavior within a composition, they assume that the
rest of the composition’s behavior adheres to the specified (full) behavior.
1.2 Problem: Unrealistic Assumptions
As the conditions, under which compositional deadlock checking approaches are
applicable, are based on unrealistic assumptions, the number of component-based
systems, to which compositional deadlock checking approaches are applicable, is
limited significantly. Requiring fully bound components conflicts with the underlying
reusability paradigm of CBSE, which often requires only parts of components or
component compositions to be reused when defining new systems [1].
A component composition can for example be instantiated differently. That is, the
set of components of the composition are configured slightly differently to be used in
different contexts. The different configurations can for example differ w.r.t. the extent
to which functionalities of the component composition are needed in a specific con-
text but share a common topology. Usually different component implementations are
used in different configurations. On the left hand side, Fig. 1 shows an excerpt from
the CoCoME example [12], which describes the component-based design of a set of
different trading systems. In the middle and on the right hand side Fig. 1 shows two
possible configurations of the component composition. While e1 includes only one
store and therefore does not make use of the functionality to dispatch products be-
tween stores or report on an enterprise level, e2 includes two stores, which are con-
nected to the product dispatcher. In e2 reporting is performed on store and enterprise
level.
Consequently, it is desirable to reuse only parts of a component by connecting only
the relevant functionalities. This, however, will likely lead to unbound or partially
bound ports, which in turn will cause only a subset of some of the components’ be-
havior to be executed. Currently, compositional deadlock checking approaches are not
applicable to compositions with partially bound ports, as their restrictive assumptions
are violated. From this the following problem can be concluded:
How can a component composition be checked for deadlock freedom, if instanc-
es of the composition can contain partial bindings?
Enterprise e1:Enterprise
pd:ProductDispatcher [1] pd:ProductDispatcher
s:PD-ST [*]
r:Reporting[1] r:Reporting
stores:Store[*] store1:Store
de:DataEnterprise[1]
pe:I-PD[0..1] [1..*] de:DataEnterprise
m:Manager[0...1
] b: CDA-Bank[1] b: CDA-Bank
ds:DataStore[1] ds:DataStore
db:DataBase[1] db:DataBase
d:Data[1] d:Data
s:Store[0..1] db:DataBase[1] db:DataBase
s:Store
db:DataBase[1] jdbsClients:Client[*] jdbsClients1:Client
e:Enterprise[0..1] db:DataBase[1] jdbsClients2:Client
e2:Enterprise
pd:ProductDispatcher
s2:PD-ST s1:PD-ST
r:Reporting store1:Store
de:DataEnterprise pe:I-PD
b: CDA-Bank
m:Manager
db:DataBase db:DataBase
ds:DataStore jdbsClients1:Client
jdbsClients2:Client
store2:Store
d:Data pe:I-PD jdbsClients3:Client
s:Store db:DataBase
b: CDA-Bank
e:Enterprise
db:DataBase
Fig. 1. Java/A-CoCoME enterprise composition specification (cf. [12]).
The remainder of this paper is structured as follows: Section 2 describes the solu-
tion idea in more detail. Section 3 presents related work. Section 4 describes the status
of the current work and section 5 gives a short summary and outlook.
2 Solution Idea
An obvious solution to the described problem is to follow a brute force approach, in
which all possible configurations with all possible combinations of partial bindings
are instantiated and checked individually with traditional deadlock checking ap-
proaches. This solution has two problems:
1. Combinatorial complexity: The possible combinations of partial bindings in a
composition result in a large space of configurations. Instantiating and verifying
all possible configurations is not possible due to this combinatorial complexity.
2. State explosion problem: Each of the instantiated configurations has to be veri-
fied with traditional deadlock checking approaches due to the partial bindings.
This implies computing the global composition behavior of each configuration
and then performing the deadlock check on the global state behavior – both,
which are subject to the state explosion problem.
So in conclusion, a brute force approach is not a viable option for verifying a com-
ponent composition if configurations with partially bound components can be derived.
Our solution idea intends to mitigate both problems and is therefore twofold.
2.1. Checking Desired Configurations
The first part of the solution idea intends to restrict the number of all possible con-
figurations to a subset, which actually should be verified. Some functionalities might
be core to a component composition, and thus it is unreasonable to exclude these
functionalities in instantiations. In the eShop example depicted in figure 1, a store
should for example always be connected to a database to allow goods to be purchased.
Furthermore, there some functionalities can depend on each other in a composition. If
the product-dispatching component (cf. Fig. 1) is for example not connected, related
functionalities, like the reporting of statistics on product dispatches will not be rele-
vant for the configuration, either. Thus, on a conceptual level there are dependencies
between functionalities, which cause some combinations of partial bindings to be
unreasonable. We propose to constrain the deadlock checking effort to a subset of
configurations, which respects these dependencies and, is thus most likely to be used.
All other configurations will be excluded from the deadlock check.
In software product line engineering (SPLE) variability modeling is a well-
established technique to specify varying properties and qualities of a system (cf. [19]).
We propose to explicitly model the subset of configurations to be verified by using
modeling techniques from SPLE. A variability model restricts the variation of a prod-
uct line by defining variation points, variants, and how the variants can be chosen and
combined. We use the concepts of variability models to specify valid combinations of
functionalities (and thus partial bindings) of compositions on a conceptual level. The
main rational for constraining the configuration space of component compositions
with variability models is that the number of options modelled in a variability model
will be smaller than the theoretically possible space of possible configurations.
Limitations of this idea: A limitation of this solution is that it possible combina-
tions of functionality to be anticipated. Thus, it still contradicts the reusability para-
digm to some extend. However, we find that this is a reasonable trade-off, since i) it is
a step towards relaxing the strict assumptions of compositional deadlock checking and
ii) we are not focusing on anticipating all combinations by explicitly enumerating
them but by explicitly stating dependencies and excluding unreasonable (and maybe
erroneous) combinations.
2.2 Removing Superfluous Behavior
The second part of the solution idea intends to make partial bindings in a configu-
ration explicit and remove the behavior, which is not executed because of those par-
tial bindings. If this superfluous behavior is removed from the behavior specifications,
compositional deadlock checking approaches are applicable to the reduced specifica-
tions. Using the variability model, it can be determined which functionalities have
been excluded from an instance. Thus, it will be possible to identify partial bindings.
In order to be able to derive behavior specifications for this configuration, which are
reduced to the actual executable behavior, the effect of partial bindings and the com-
bination of partial bindings onto the composition’s behavior has to be analyzed.
We propose to identify and explicit specify these dependencies between partial
bindings and the behavior of components in a behavior reduction model. Such a mod-
el can then be used to reduce the behavior specifications using existing model slicing
techniques, where the partial bindings can be used as slicing criteria. Accordingly,
such a model needs to provide means to relate the absence of functionality in a con-
figuration (using the variability model and structural specification) to parts of the
behavior specification. Furthermore, the notation needs to be compatible with existing
slicing techniques. The resulting behavior specifications can then be used as input to
existing compositional deadlock techniques. Thus, the state explosion problem is
mitigated for the set of configurations, which is supposed to be verified.
Limitations of this idea: A risk to the proposed solution is that additional effort will
be needed to generate the behavior reduction model and compute the reduced specifi-
cations. However, since the reduction model only has to be created once, we work
under the hypothesis that the high number of derivable instances, in which the reduc-
tion model can be reused and for which the computation and analysis of the global
state space can be avoided, will outweigh the extra effort. However, an experiment
will be conducted in order to determine whether this hypothesis holds.
Fig. 2 shows an abstract sketch of the solution idea. It can be seen that the variabil-
ity model will solely be related to the structural specification of the composition. The
behavior reduction model is based on the behavior of the individual components and
uses information from the structural specification as well as the variability model to
enrich the behavior information.
Fig. 2. Abstract solution sketch.
3 State-of-the-Art: Compositional Deadlock Checking
Deadlock-freedom is generally non-compositional: if components are deadlock free in
isolation, they still might deadlock in a composition due to interactions making it
challenging to find a sufficient condition to relate global and local deadlock-freedom.
Existing compositional deadlock checking approaches can be differentiated into de-
ductive and assume-guarantee reasoning approaches as described in the following.
3.1 Deductive Deadlock Checking
In summary, most deductive approaches focus on the pairwise behavioral equivalence
between the behavior of connected components. Under the assumption that the com-
ponents are deadlock free and that the interaction behavior is deadlock free, the analy-
sis of the behavioral equivalence is a sufficient property to guarantee the local dead-
lock freedom of components and thus also the global deadlock freedom. Martens and
Majster-Cederbaum’s approach [10, 13, 14, 15] checks connected components for
example pairwise for potential deadlocks. The reachability of those potential dead-
locks is analyzed compositionally. The approach can only deal with tree like topolo-
gies. Although the approach theoretically allows for partial bindings, it is not e able to
detect deadlocks that occur due to dependencies between several partial bindings.
In contrast, the approach presented by Aldini and Bernardo [2, 3, 7] also can also
deal with cycles in arbitrary topologies. It is assumed that every topology can be re-
duced to an acyclic topology by reducing cycles into a new component. While the
connections between the components are verified compositionally for the non-cyclic
part, for the cyclic part they have to perform more extensive checks to assure that
there are no cyclic dependencies between the components causing a deadlock. How-
ever, they avoid computing the “global” behavior of the components involved in the
cycle by instead analyzing the communications paths within the cycle using a weak
bisimulation equivalence relation. In contrast to Martens and Majster-Cederbaum
their approach requires full bindings within a composition.
Choi and Kim’s approach also assumes full binding of components in a composi-
tion [9]. It is based on controlled composition and abstraction. The approach provides
a smaller behavior specification of a composite component by removing synchronized
interaction in a parallel composition and removing the internal behavior of composite
components via projection abstraction. The verification is performed compositionally
for each component, whereas the dependencies towards the environment are consid-
ered by explicitly considering/providing drivers that can generate events and stubs
that consume events. If each component behaves correctly under the assumption of a
correct environment, the composition is be deadlock free.
Zeng and Miao [22] also propose an approach that is based on abstraction and
compositional reasoning. As abstraction and compositional reasoning do not preserve
deadlock freedom, the authors extend the notion of transitions in LTSs by classifying
transitions into certain and uncertain transitions. The deadlock detection considers this
differentiation and is performed using the CEGAR (counterexample guided abstrac-
tion refinement) framework. Even though the approach claims that it is compositional,
their verification is not as it is based on the parallel composition of the abstractions.
Hennicker et al. [11, 12] propose an approach, which can compositionally assure
deadlock freedom of a central component in a star topologies if at most one port of
that component is behavioral restricted (partially bound). The approach is based on
I/O transition systems and checks pairwise the behavior at connected ports fro dead-
lock freedom assuming that each component is deadlock free in isolation. The pre-
sented approach explicitly takes into account that components do not necessarily have
to be fully bound, i.e. that expected behavior is not provided by the connected com-
ponent. Hennicker et al. compute the parallel composition when more than one behav-
ioral restriction is found. However, they only use the central component of the star
topology and the ports at which behavioral restrictions occurred in the composition.
Thus, they use the interaction behavior specification to detect behavioral restrictions
and then directly check for deadlocks in the reduced global state space.
3.2 Assume-Guarantee Reasoning (AGR).
The idea of AGR [18] is to verify a component using an artificial environment that is
based on the assumptions the component has about its environment. Using such an
artificial environment reflecting the assumptions of a component, allows for an early
verification of the component. Approaches focusing on how to use AGR for deadlock
detection assume the parallel composition of two components to be deadlock free if
the parallel composition of a component and its artificial environment is deadlock free
and the other component “adheres” to the environment specification [8].
Chaki and Shina [8] for example propose a compositional deadlock detection algo-
rithm that uses learning-based automated AGR. Their formalism is based on an au-
tomata-theoretic representation of failure traces. The deadlock detection is performed
pairwise on failure automata and checks for inclusion in the specification language.
They use an AGR rule, which uses the composition of a failure automaton with its
assumption specification and then checks that a second automaton is included in the
language of the assumptions.
Parizek and Plasil [16] propose several options to generate an artificial environ-
ment using AGR. The possibility to use only a subset of the functionality in the as-
sumption specification enables the partial binding of components but all partial bind-
ings have to be anticipated when specifying the assumptions.
Bensalem et al. [4, 5, 6] propose an approach for the compositional verification of
components, which uses inductive reasoning as well as AGR. The approach is based
on i) component invariants, which are an over-approximation of components’ reacha-
bility sets and ii) interaction invariants, which are global constraints over the states of
components involved in interactions. The overall algorithm sequentially computes a
system invariant using the interaction and component invariants. If it cannot be shown
that the desired invariant holds, a stronger invariant is computed or the calculation is
stopped with inconclusive output. Like in the approach of Martens and Majster-
Cederbaum, components can be partially reused. However, they do not discuss the
problems, which could occur due to partial bindings nor is it obvious how the algo-
rithm would be affected.
Generally, AGR approaches do not make any assumptions about the topology of a
composition as long as the specified assumptions are satisfied. They allow the as-
sumption specifications to be only a subset of the offered functionalities and thus
allow partial bindings. However, any partial binding has to be anticipated and existing
verification approaches do not explicitly check for deadlocks due to missing bindings.
4 Work in Progress
The research methodology we use, follows the idea of the design science research
methodolgy and follows the six-step process model proposed by Peffers et al. [17].
The work currently in progress focuses on step 3 „Design and Development“, i.e. on
developing an approach according to the two solution ideas. The work, which has to
be performed as part of step 3 can be grouped according to the two core ideas of the
solution idea as described in the following.
4.1 Part 1: Restricting the Combination Space
Step 1.1 Identification of appropiate means to restrict the configuration space. In
order to restrict the configuration space of a component configuration which can be
realized with partial bindings, an appropiate modeling notation has to be selected. As
described in sect. 2, variability modeling as it is used in SPLE shows similarities with
this objective and has therefore been selected as appropiate modeling means. Due to
existing reasearch performed in our research group, the proposed approach is based
on the Orthogonal Variability Model [19].
Step 1.2 Identification of variation in component compositions. In order to restrict
the configuration space, it needs to be understood how configurations can vary and
which elements of a composition are affected by unused functionality. Furthermore,
the conceptual dependencies between functionalities need to be taken into account in
this analysis. Different cases of variation have been identified in this step.
Step 1.3 Definition of artifact dependencies between the variability model and
the composition. In SPLE, artifact dependencies describe the relation between devel-
opment artifacts and the variability model and, therefore, determine, which develop-
ment artifacts become part of a derived product [19]. The approach presented here
also has to define artifact dependencies between the variability model and the compo-
nent composition covering the cases identified in step 1.2. In SPLE a large number of
approaches exist, which model variability in component compositions. These ap-
proaches distinguish between coarse grained variability (i.e. only the complete
component can vary) and fine grained varaibility (i.e. single functionalities of a
component can vary) in the component compositions. The approach proposed by this
paper adopts a fine grained solution. The artifact dependencies have been specified
formally extending the formal component model underlying the approach.
4.2 Part 2: Removing Superfluous Behavior
Step 2.1 Identification of the affect of partial bindings on behavior specifications.
In order to remove superfluous behavior it has to be analysed how partial bindings
can affect the behavior of a component. In this step, different cases have been
identified, which differentiate between the partial binding of provided and required
functionalities and which also consider the combination of several partial bindings
and the implicit propagation of superfluous behavior onto other components.
Step 2.2 Identification of an appropiate modeling notation for the behavior
reduction model. In order to allow superfluous behavior to be removed from
behavior specifciations, an appropriate notation needs to be found for the behavior
reduction model. Such a notation needs to meet the following requirements: i) it
should be usable as input to existing model slicing techniques, ii) a relation between
the variability model and the behavior reduction model needs to be defined in order to
use the information of the variability model about the absence of functionalities and
iii) the behavior reduction model also needs to use information from the structural
specification about ports affected by the absence of functionalities.
Step 2.3 Definition of an algorithm to identify and remove superfluous behavior.
Finally an algorithm needs to be defined, which allows an efficient identification of
all cases defined in step 2.1 while considering the propagation between components
and which also allows to remove superfluous behavior for a concrete composition.
5 Summary and Outlook
The paper motivates and describes a solution idea for allowing compositional
deadlock checking approaches to be applied to compositions, which can be realized
with partial bindings. The proposed approach is based on two core ideas: i) restrict
the number of configurations that can be derived and have to be verified and ii) re-
move behavior that is not executed due to partial bindings.
The resulting behavior specifications can be used as input to existing composition-
al deadlock techniques. While first results have been achieved in defining the ap-
proach, the next step has to focus on defining the behavior reduction model and defin-
ing the algorithm for identifying and removing superfluous behavior before the ap-
plicability of the approach as well as the runtime experiments can be conducted.
The applicability of the approach will be illustrated with the CoCoME case study.
Potential partial bindings will be analyzed for CoCoME and restricted with a variabil-
ity model. An analysis of the number of all possible configurations in comparison to
the number of restricted configurations will be conducted to demonstrate the useful-
ness of restricting the configuration space. In addition, the performance of the ap-
proach will be evaluated with experiments. These experiments will focus on analyz-
ing the efficiency of the behavior reduction algorithm and compare the performance
of compositional deadlock checking on reduced behavior specifications to the compu-
tation and analysis of the global state space for each possible configuration. A random
subset of the derivable configurations of the CoCoME case study will be used as input
to those experiments. The runtime will be compared to the runtime of traditional
deadlock checking approaches, which compute the global system behavior using the
same subset of configurations.
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