Towards Semantic KPI Measurement

Linked Data (LD) represent a great mechanism towards integrating information across disparate sources. The respective technology can also be exploited to perform inferencing for deriving added-value knowledge. As such, LD technology can really assist in performing various analysis tasks over information related to business process execution. In the context of Business Process as a Service (BPaaS), the first real challenge is to collect and link information originating from different systems by following a certain structure. As such, this paper proposes two main ontologies that serve this purpose: a KPI and a Dependency one. Based on these well-connected ontologies, an innovative Key Performance Indicator (KPI) analysis system is then built which exhibits two main analysis capabilities: KPI assessment and drill-down, where the second can be exploited to find root causes of KPI violations. Compared to other KPI analysis systems, LD usage enables the flexible construction and assessment of any KPI kind allowing experts to better explore the possible KPI space

A Cross-layer Monitoring Solution based on Quality Models

In order to implement cross-organizational workflows and to realize collaborations between small and medium enterprises (SMEs), the use ofWeb service technology, Service-Oriented Architecture and Infrastructure-as-a- Service (IaaS) has become a necessity. Based on these technologies, the need for monitoring the quality of (a) the acquired resources, (b) the services offered to the final users and (c) the workflow-based procedures used by SMEs in order to use services, has come to the fore. To tackle this need, we propose four metric Quality Models that cover quality terms for the Workflow, Service and Infrastructure layers and an additional one for expressing the equality and inter-dependency relations between the previous ones. To support these models we have implemented a cross-layer monitoring system, whose main advantages are the layer-specific metric aggregators and an event pattern discoverer for processing the monitoring log. Our evaluation is based on the performance and accuracy aspects of the proposed cross-layer monitoring system

A specification-based QoS-aware design framework for service-based applications

Effective and accurate service discovery and composition rely on complete specifications of service behaviour, containing inputs and preconditions that are required before service execution, outputs, effects and ramifications of a successful execution and explanations for unsuccessful executions. The previously defined Web Service Specification Language (WSSL) relies on the fluent calculus formalism to produce such rich specifications for atomic and composite services. In this work, we propose further extensions that focus on the specification of QoS profiles, as well as partially observable service states. Additionally, a design framework for service-based applications is implemented based on WSSL, advancing state of the art by being the first service framework to simultaneously provide several desirable capabilities, such as supporting ramifications and partial observability, as well as non-determinism in composition schemas using heuristic encodings; providing explanations for unexpected behaviour; and QoS-awareness through goal-based techniques. These capabilities are illustrated through a comparative evaluation against prominent state-of-the-art approaches based on a typical SBA design scenario

1 A Survey on Service Quality Description

Quality of service (QoS) can be a critical element for achieving the business goals of a service provider, for the acceptance of a service by the user, or for guaranteeing service characteristics in a composition of services, where a service is defined as either a software or a software-support (i.e., infrastructural) service which is available on any type of network or electronic channel. The goal of this article is to compare the approaches to QoS description in the literature, where several models and metamodels are included. consider a large spectrum of models and metamodels to describe service quality, ranging from ontological approaches to define quality measures, metrics, and dimensions, to metamodels enabling the specification of quality-based service requirements and capabilities as well as of SLAs (Service-Level Agreements) and SLA templates for service provisioning. Our survey is performed by inspecting the characteristics of the available approaches to reveal which are the consolidated ones and which are the ones specific to given aspects and to analyze where the need for further research and investigation lies. The approaches here illustrated have been selected based on a systematic review of conference proceedings and journals spanning various research areas in compute

Extending OWL for QoS-based Web Service Description and Discovery 1 Main Theme of Thesis

and programming language-agnostic software applications that can be advertised, located and used across the Internet. They are viewed as one of the promising technologies that could help business entities to automate their operations on the web on a large scale by automatic discovery and consumption of services. Based on the above reasons, the WS paradigm is being adopted by many companies and individuals and many WSs are being deployed and running. However, as all of these WSs are advertised in a UDDI-based repository, an unavoidable fact as UDDI is a de-facto standard, the problem of discovering them based on a requester’s functional needs becomes crucial. UDDI uses a syntaxbased approach for WS description leading to purely syntactic discovery efforts returning imprecise and inaccurate results. OWL-S [OWL-S Coalition 2003] and similar joint Semantic Web and WS efforts solve the problem of syntactic WS description by using ontologies for describing WSs. Ontologies provide meaning to concepts and relationships between them, leading to semantic WS Discovery algorithms, which provide more precise and accurate results

Βασισμένη σε ποιότητα υπηρεσίας περιγραφή και ανακάλυψη διαδικτυακών υπηρεσιών

The success of the /Web Service/ (WS) paradigm has led to a proliferation of available WSs. As these WSs are advertised in registries, they have to be discovered based on user needs. However, these registries rely on the current WS technology stack that uses /WSDL/ and /UDDI/ for WS description and discovery. Unfortunately, these two languages rely on syntactic descriptions of WS functional and non-functional attributes. This situation creates two problems. Firstly, syntactic discovery efforts return inaccurate results. Secondly, no means are provided in order to select among multiple WSs that perform the same function. The first problem has been solved by combining /Semantic Web/ (SW) and WS technologies. The second problem can be solved by taking into account a big subset of all non-functional properties of WSs, which is called /Quality of Service/ (QoS). QoS is closely related with the performance of a WS so it has a substantial impact on user's expectations from a WS and can be used as a discriminating factor between functionally equivalent WS advertisements. Thus WS descriptions must be enhanced with QoS descriptions. Additionally, WS discovery algorithms should perform QoS-based /filtering/ (matchmaking) and /ranking/ (selection) on WS advertisements in order to produce fewer ranked results. A /QoS offer/ (or /demand/) of a WS is a set of constraints on some QoS attributes. Actually, the current modeling efforts of QoS specifications only differ in the expressiveness of these constraints. However, when it comes to QoS attributes modeling, these efforts fail. The main reason is that they use a poor, syntactic and inextensible QoS attributes model. Based on the above problem, the first part of this thesis is dedicated to conducting a research on all QoS-based WS description efforts in order to unveil those features that are necessary for a QoS description model of WSs. The result is a set of requirements for a rich, semantic and extensible QoS-based WS description model. Based on these requirements, an ontology language called /OWL-Q/ has been carefully created by extending OWL-S. One disadvantage of using ontologies is the creation of different descriptions of the same concept. Concerning the QoS domain, this can be true for QoS metrics. We argue that the state-of-the-art ontology alignment algorithms cannot be used in this case because of the use of mathematics for deriving complex QoS metrics from simpler ones. For this reason, we have devised a twofold solution to this problem: a) a semantic QoS metric matching algorithm and b) based on this algorithm, an alignment algorithm for aligning OWL-Q descriptions of WS providers and requesters. There are two main approaches for QoS-based WS matchmaking: ontology-based and /Constraint Programming/ (CP)-based but both of them present some major drawbacks. In this thesis, we argue that the CP-based approach is better but has to be enhanced in many ways. The first enhancement is the use of an appropriate solving technique depending on the type of constraints present in QoS-based WS specifications. The second enhancement is the use of correct matchmaking metrics. Another enhancement is the use of optimization techniques especially for over-constrained demands. All implemented matchmaking algorithms were evaluated based on a testing framework producing random QoS-based WS descriptions. A final contribution of this thesis was a QoS-based WS selection algorithm overcoming the disadvantages of all other research approaches. Thus, as can be seen from the totality of the above contributions, a semantic framework for QoS-based WS description and discovery was produced in terms of this thesis.Η επιτυχία του παραδείγματος των Διαδικτυακών Υπηρεσιών (ΔΥ) έχει οδηγήσει σε πολλαπλασιασμό των διαθέσιμων ΔΥ. Καθώς αυτές οι ΔΥ δημοσιοποιούνται σε αποθήκες, πρέπει να ανακαλυφθούν με βάση τις ανάγκες των χρηστών. Όμως, αυτές οι αποθήκες βασίζονται στη τρέχουσα στοίβα τεχνολογίας ΔΥ, η οποία χρησιμοποιεί τις γλώσσες /WSDL/ και /UDDI/ για την περιγραφή και ανακάλυψη ΔΥ. Δυστυχώς, αυτές οι δύο γλώσσες βασίζονται στη συντακτική περιγραφή λειτουργικών και μη ιδιοτήτων των ΔΥ. Αυτή η κατάσταση δημιουργεί δύο προβλήματα. Πρώτον, οι βασιζόμενες σε συντακτικά μοντέλα ερευνητικές προσπάθειες επιστρέφουν μη ακριβή αποτελέσματα κατά την ανακάλυψη ΔΥ. Δεύτερον, δεν υπάρχει μέσο επιλογής της καλύτερης ανάμεσα σε πολλαπλές ΔΥ που προσφέρουν την ίδια λειτουργικότητα. Το πρώτο πρόβλημα έχει λυθεί με το συνδυασμό τεχνολογιών /Σημασιολογικού Δικτύου/ (ΣΔ) (Semantic Web) και ΔΥ. Το δεύτερο πρόβλημα μπορεί να λυθεί λογαριάζοντας ένα μεγάλο υποσύνολο μη λειτουργικών ιδιοτήτων των ΔΥ που ονομάζεται /Ποιότητα Υπηρεσίας/ (ΠΥ) (Quality of Service). Η ΠΥ έχει στενή σχέση με την απόδοση των ΔΥ. Επομένως, η ΠΥ έχει ουσιώδη αντίκτυπο στις προσδοκίες των χρηστών από μια ΔΥ και μπορεί να χρησιμοποιηθεί ως παράγοντας διαχωρισμού ανάμεσα σε λειτουργικά ισοδύναμες περιγραφές ΔΥ. Συνεπώς, οι περιγραφές ΔΥ πρέπει να εμπλουτιστούν με περιγραφές ΠΥ. Επιπροσθέτως, οι αλγόριθμοι ανακάλυψης ΔΥ πρέπει να επιτελούν φιλτράρισμα και ταξινόμηση των ΔΥ με βάση την ΠΥ ώστε να παράγουν λιγότερα και ταξινομημένα αποτελέσματα. Μια προσφορά ή ζήτηση ΠΥ μιας ΔΥ είναι ένα σύνολο από περιορισμούς σε ορισμένες ιδιότητες ΠΥ. Στην πραγματικότητα, οι τρέχουσες προσπάθειες μοντελοποίησης των προσδιορισμών ΠΥ διαφέρουν μόνο στην εκφραστικότητα των εν λόγω περιορισμών. Όμως, όσον αφορά των μοντελοποίηση των ιδιοτήτων ΠΥ, οι τρέχουσες ερευνητικές προσπάθειες αποτυγχάνουν διότι χρησιμοποιούν ένα φτωχό, συντακτικό και στατικό μοντέλο ιδιοτήτων ΠΥ. Με βάση το παραπάνω πρόβλημα, το πρώτο μέρος αυτής της διατριβής πραγματεύεται την διεξαγωγή έρευνας σε όλες τις βασιζόμενες σε ΠΥ προσπάθειες περιγραφής ΔΥ ώστε να αποκαλύψει εκείνα τα χαρακτηριστικά που είναι απαραίτητα για ένα μοντέλο περιγραφής ΔΥ βασιζόμενο σε ΠΥ. Το αποτέλεσμα είναι ένα σύνολο από απαιτήσεις για πλούσιες, σημασιολογικές και επεκτάσιμες περιγραφές ΠΥ για ΔΥ. Με βάση τις παραπάνω απαιτήσεις, μια γλώσσα οντολογίας με όνομα ΟWL-Q δημιουργήθηκε επεκτείνοντας την γλώσσα OWL-S. Ένα σημαντικό μειονέκτημα της χρήσης οντολογιών είναι η δημιουργία διαφορετικών περιγραφών για μια οντότητα. Όσον αφορά το πεδίο γνώσης της ΠΥ, αυτό μπορεί να συμβαίνει για τις μετρικές ΠΥ. Υποστηρίζουμε ότι οι τελευταίας τεχνολογίας αλγόριθμοι ευθυγράμμισης οντολογιών δεν μπορούν να χρησιμοποιηθούν στην προκειμένη περίπτωση λόγω της χρήσης των μαθηματικών στην παραγωγή πολύπλοκων μετρικών ΠΥ από πιο απλές μετρικές. Για αυτό τον λόγο, έχουμε επινοήσει μια διπλή λύση σε αυτό το πρόβλημα: α) ένα σημασιολογικό αλγόριθμο ταιριάγματος μετρικών ΠΥ, β) με βάση αυτόν τον αλγόριθμο, ένα αλγόριθμο ευθυγράμμισης των OWL-Q περιγραφών. Υπάρχουν δύο κύριες προσεγγίσεις για το ταίριαγμα ΔΥ με βάση την ΠΥ: οντολογικές και βασισμένες στον Προγραμματισμό με Περιορισμούς (ΠΠ) (Constraint Programming) που όμως παρουσιάζουν σημαντικά μειονεκτήματα. Σε αυτή τη διατριβή υποστηρίζουμε ότι η δεύτερη προσέγγιση είναι καλύτερη αλλά πρέπει να επεκταθεί σε πολλές κατευθύνσεις. Η πρώτη επέκταση είναι η χρήση κατάλληλης μεθόδου επίλυσης περιορισμών ανάλογα με το είδος των περιορισμών που περιέχονται στις περιγραφές ΠΥ. Η δεύτερη επέκταση είναι η χρήση σωστών μετρικών ταιριάγματος. Μια άλλη επέκταση είναι η χρήση τεχνικών βελτιστοποίησης ειδικά για την περίπτωση υπερ-περιορισμένων αιτημάτων χρηστών. Όλοι οι αλγόριθμοι ταιριάγματος αποτιμήθηκαν εμπειρικά με τη χρήση ενός πλαισίου πειραμάτων το οποίο παρήγαγε τυχαίες περιγραφές ΠΥ για ΔΥ. Μια τελευταία συνεισφορά αυτής της διατριβής είναι ένα αλγόριθμος επιλογής ΔΥ βασισμένος σε ΠΥ, ο οποίος επιλύει όλα τα προβλήματα που παρουσιάζουν οι άλλες ερευνητικές προσεγγίσεις. Συνεπώς, όπως μπορεί να φανεί από το σύνολο των συνεισφορών, ένα σημασιολογικό πλαίσιο για την περιγραφή και ανακάλυψη ΔΥ με βάση την ΠΥ αναπτύχθηκε στα πλαίσια της εν λόγω διατριβής

Towards Optimizing the Non-Functional Service Matchmaking Time

The Internet is moving fast to a new era where million of services and things will be available. In this way, as there will be many functionally-equivalent services for a specific user task, the service non-functional aspect should be considered for filtering and choosing the appropriate services. The related approaches in service discovery mainly concentrate on exploiting constraint solving techniques for inferring if the user non-functional requirements are satisfied by the service nonfunctional capabilities. However, as the matchmaking time is proportional to the number of non-functional service descriptions, these approaches fail to fulfill the user request in a timely manner. To this end, two alternative techniques for improving the non-functional service matchmaking time have been developed. The first one is generic as it can handle non-functional service specifications containing n-ary constraints, while the second is only applicable to unary-constrained specifications. Both techniques were experimentally evaluated. The preliminary evaluation results show that the service matchmaking time is significantly improved without compromising matchmaking accuracy

Towards Combined Functional and Non-Functional Semantic Service Discovery

Service-orientation is increasingly adopted by application and service developers, leading to a plethora of services becoming increasingly available. To enable the construction of applications from such services, the respective description and discovery of services must be supported. Both functional and non-functional aspects should also be considered as they play a significant role in the service management lifecycle. The focus in state-of-the-art service discovery has been mainly on one aspect and not both of them. As such, this paper aims at investigating the issues involved in considering both functional and non-functional aspects in service discovery. In particular, it proposes different ways via which aspect-specific algorithms can be combined to generate a complete service discovery system. It also proposes a specific unified service discovery architecture. Finally, it evaluates the proposed algorithms with respect to their performance to give valuable insights to the reader