Towards automated composition of convergent services: A survey
Introduction
The telecommunication and computer network industries are facing a great shift from atomic services (e.g., voice and email) towards much more dynamic, convergent services, such as unified social networking and integrated video conferencing. Under this premise, telco and computer network operators need to transform themselves from simple operators into services aggregators carrying the duty of providing services that bring together numerous applications from a variety of sources [1].
The term “convergent” has been used widely in telecommunication and computer networks with two meanings: to describe the fusion of fixed and mobile services [2], or as a synonymous of the Next Generation Network (NGN) that is a packet-based network able to transport all type of information and services, like voice, data, and video, integrating traditional telephony networks and Internet [3]. In this paper, we use the term “convergent” as efficient coexistence of services available on the Telecom (e.g., voice and video calls with reverse charging offered by telco operators like Orange and Movistar) and Web (e.g., services of maps and RSS feeds offered by big Internet players like Google and Yahoo) domains to provide more services to the user.
Telecom services can be created by using Services Creation Environments (SCE) [4] and Mashup Development Environments (MDE) [5], [6] that allow the users (e.g., programmers and administrators of telco and/or computer networks) to combine the functionalities of heterogeneous services using drag-and-drop and wire tools for composing new services. Such a way of carrying out service composition is valid as long as the number of traditional communication services is low and the reliability of services is high enough ( > 99%) so they do not change continually [7].
In the case of the convergent service composition, that involve atomic services from the Web and Telecom domains, such services may change their interfaces, become available or unavailable, and their number may also grow to unmanageable sizes. Both the dynamic nature of services offered by the Web and the sheer amount of relevant services that may be available on it for a given task hinder greatly the use of approaches offering semi-automated service composition (i.e., composition based on MDEs and SCEs). If time is a crucial factor, semi-automated service composition may become inefficient, which raises the need of approaches able to perform fully-automated service composition.
Automation is defined as the delegation of tasks to machine or computer systems, thus reducing procedural load and freeing operators from vigilance over routine and tedious tasks [8]. Several approaches have appeared to fully automate the composition of services available in the Web from both academia [9], [10], [11], [12], [13], [14] and industry [15], [16]. Similarly, some research has revolved around fully automation of communication service composition, coming mainly from European Projects [17], [18]. Considering the evolution of service composition in the Telecom and Web domains, we raise the first research question addressed in this paper: Which is the level of automation that has been achieved to date from previous service composition approaches?
In addition to the aforementioned automation, it is important to consider that the service composition carried out in the Telecom fundamentally different of the conducted in the Web, which means that some technical issues must be contemplated when combining services from both domains [19], [20]. Moreover, several other characteristics pertaining to specific application domains, like user preferences, response time, adaptability, and scalability must be taken into account. This is because the fact that convergent service composition often involves the challenge of merging two areas of knowledge with their respective concepts, technologies, and architectures. For this reason, a systematic way of analysing the strengths and weaknesses of each existing solution for a particular application domain is needed. In this way, we raise the second research question addressed in this paper: which elements must be considered for applying automated services composition in different specific domains?
Convergent service composition is also a complex process that often involves several elaborated steps or phases, from processing the input to selection of services to its execution. As these phases often focus on one or more aspects of the service composition process, it is needed to classify them. In this way, we raise the third research question addressed in this paper: which are the phases for convergent service composition and the approaches useful in each one of them?
The above raised research questions indicate that building up a convergent service is not trivial, because although there are significant approaches that aim to automate the service composition at different levels in the Web, telco networks, and computer networks, selecting the most appropriate approach(es) for specific case studies is complex due to the big amount of involved information and the lack of technical considerations. Thus, in this paper, we identify the relevant phases for convergent service composition and explore the existing approaches and their associated technologies for automating each phase. For each technology, the maturity and results are analysed, as well as the elements that must be considered prior to their application in real scenarios. Furthermore, we provide research directions in the convergent service composition phases.
The research conducted to answer the raised questions led to the following contributions:
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Identify the relevant phases for convergent service composition.
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Explore and analyse the existing approaches and their associated technologies for automating each phase.
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Provide research directions in each one of convergent service composition phases.
The remainder of this paper is organised as follows. In Section 2, we present the methodology followed to build up this survey. In Section 3, we review foundations about service composition. In Section 4, we introduce the phases for convergent service composition. In Sections 5–7, we describe and discuss each phase and its associated approaches. In Section 8, we present research directions. Finally, in Section 9, we provide some conclusions that help to select approaches for convergent service composition.
Section snippets
Methodology
To solve the research questions, we follow the next steps [21]: (i) formalize the service composition process by defining different phases, (ii) classify the existing approaches under the umbrella of requirements and criteria for their application in convergent composition; and (iii) define the guidelines for employing diverse approaches and their technologies in convergent service composition.
In this paper, we carry out a comparative literature review [22], aiming to identify the existing
Foundations on service composition
In this section, we introduce the concepts of service composition and convergent service composition. Furthermore, we present the differences among the services offered in the domains of Telecom and Web as well as current approaches for describing such services.
Convergent service composition
In a general sense, the process for carrying out convergent service composition can be decomposed in several relatively independent steps, beginning with the user request and ending with the execution of the composite service. The whole process (see Fig. 8) can thus be divided into four phases: creation, generation, adaptation and execution.
An important consideration to be noted is that the automation of each phase is independent of the automation of the rest of the other phases. This means
Service creation
As afore defined, service creation is the process of translating the user request to a language or descriptor understandable by the computer. For instance, the translation may be done from the request expressed in natural language to BPEL/Bite language or to executable code. This phase depends largely on the level of expertise and the device used by the user. If the user is an expert and uses a desktop personal computer, a graphical interface for creating workflows is very suitable. On the
Service generation
As above described, the service generation is related to the creation/composition of a chain or a linked set of services that can be represented as a business process encoded, for instance, in BPEL or BPEL for REST. There exists a broad range of research approaches around the topic of automated/semi-automated service composition in the Web domain, most of which is applicable to convergent composition. Such approaches can be divided into two categories: workflow-based approaches and approaches
Service adaptation and execution
In this section, at starting, we present approaches about the service adaptation phase. Later, we present research addressing the service execution and reconfiguration phases.
Research directions
From the above review, we can see that many advances have been made in various research aspects, including automated generation, graphical creation, and execution of convergent services in telecom environments. However, there are still many open research issues that need to be solved before the automated composition can be of practical use. This section presents the research directions and how existing approaches can be used or contribute to address the challenges of convergent service
Conclusions
Selection of technologies for specific convergent composition solutions is complex due to the big amount of considerations. In this paper, we have identified the relevant phases for convergent service composition and explored the existing approaches for automating each one of these phases. It has been analysed that all phases of convergent composition have reached high level of automation using different approaches. Following, as conclusion, we provide general guidelines that help to select the
Acknowledgements
The research of PhD(c) Caicedo is supported by the PECPG (Agreement Program Students Graduate) of the CAPES (Brazil) and the University of Cauca (Colombia).
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