In fact, service quality can play an important role in several phases of the service life cycle [Kritikos and Plexousakis 2009]. As described in Section 2, SQM focuses on the analysis of a set of quality attributes that are considered important in service applications. The results of the evaluation of the reviewed SQMs according to the comparative criteria are shown in Table II.
Overall Analysis
Data quality is a multi-dimensional concept that defines the suitability of the data used for the application involved. The most important and representative data quality characteristics (according to the data quality survey) are accuracy, completeness, consistency and timeliness.
SERVICE QUALITY METAMODELS 1. Background
Methodology and Analysis
Based on the SQMM categorization of the previous subsection, there are actually three SQMM divisions: pure, SLA-enabled, and security-based. The assessment of this criterion for a specific SQMM depends on the SQMM's satisfaction of the nine sub-criteria analyzed previously. The richness of SQMM metric models was evaluated according to the following metric aspects.
Thus, if SQMM does not meet any of the previous requirements, then its expressivity is poor. Indeed, based on the analysis of the previous criterion, pure SQMMs have increased their expressiveness over the years. On the other hand, WSDL is the most referenced SFSL in the remaining SQMM partitions.
If the answer is positive, it means that the SQMM has actually been used in any of the service lifecycle activities (except the first one). Most SLA-compliant SQMMs, apart from WSLA, are not used in an implemented negotiation framework.
Overall Analysis
In addition, in relation to the results of the previous criterion, all SQMMs agree that pattern matching rules are used in service discovery implementation, thus realizing the need to increase the accuracy of service discovery activity. Thus, the service negotiation activity is the stopping point of using QSDs and the corresponding starting point of SLAs. Since many of the proposed ontology-based SQMMs are not publicly available, we only have a description of the modeled concepts and their attributes and relationships.
Before presenting the results of the comparison of the ontology-based SQMMs based on the preceding criteria, it should be indicated that the following restrictions have been imposed to ensure the fairness of the comparison: (a) only the upper ontology, which actually maps to the respective SQMM, of an approach was considered and not the mid- and low-level ontologies that map to concrete domain-independent and domain-dependent quality terms, respectively, and (b) unnamed classes were not considered. The results of the assessment of the complexity and coherence of the ontology-based SQMMs are shown in Table VII. This was also indicated by the analysis of the second, third and fourth comparison criteria in Section 4.2.
This can be justified by their inability to model specific SLA constructs, which are considered more useful for supporting the rest of the service life cycle activities. The next section explains this role and provides an analysis of the capabilities of SLA languages in relation to their support of service life cycle activities.
SERVICE-LEVEL AGREEMENTS 1. Background
Methodology and Analysis
For this reason, this section neglects from its analysis the quality description properties of the SLA languages. The evaluation results of the investigated languages according to our selected criteria are presented in Tables X and XI. Ultimately, there is an overall analysis of the service contract and SLA languages across all criteria.
Finally, a general analysis of the ability of the SLA languages to support this SLA management lifecycle activity is provided. The evaluation results are displayed in the first row of the Negotiation lifecycle activity of Tables X and XI. Apart from the main SLO condition (clause) which is modeled in all SLA/service contract languages, other important SLA assessment information to be modeled is: (a) Condition Assessor, (b) Qualifying Condition, (c) Obligatory Party, (d )Rating Schedule, (e) Validity Period and (f) Corrective Action.
The assessment results are presented in the first row of the Life Cycle Activity Assessment of Tables X and XI. The assessment results are presented in the fifth row of the Assessment life cycle activity of Tables X and XI. The assessment results are presented in the first row of the repayment life cycle activity of Tables X and XI.
The evaluation results are presented in the last row of settlement life cycle activities in Tables X and XI.
Overall Analysis
In the second case, the SLA must determine this maximum number of service calls, and none of the existing languages are able to model this information. In this case, the SLA is first archived and then disposed of when a specific statutory period has expired. So, for this activity, each language is only evaluated based on its ability to model the SLA validity period.
Although the modeling of an SLA's (service contract) validity period is very important, less than half of the languages are able to offer it. Regarding each partition separately, there is a balance between SLA languages that support and do not support modeling this information. So the SLA language designers begin to understand the need to model this information, while the corresponding SCL designers do not.
From the SCL side, this conclusion can be explained by considering that these languages are designed with a focus on functionality and not quality. Since the functionality does not change that much, it is therefore not necessary to model the validity period of the service contract explicitly.
CONCLUDING REMARKS AND FUTURE WORK
Discussion on Service Quality Models
In this way, the service monitoring, assessment and adjustment activities can exploit them to perform dependency analysis in order to detect incorrect monitoring facts and discover the components of the same or different layer that caused an SLO violation. However, since the service output is mostly composed of information, data quality can be considered a part of service QoS and can thoroughly drive the analysis of the required input and provided output. This SQM can therefore be used to annotate QSDs and SLAs that can be used across all service life cycle activities, but in specific scenarios.
Most of the remaining approaches provide a metric description for some of the attributes involved, which does not contain a precise evaluation formula, but a set of evaluation rules. Since the final rules can be further used to create precise estimation formulas, these approaches can be used in all activities of the service life cycle, if properly extended. Based on the previous analysis, no SQM can be considered optimal according to its evaluation for all the obtained criteria.
In fact, for particular divisions of comparison aspects, different approaches stand out as the best. Thus, a new SQM is needed that should combine the characteristics of the best approaches in all aspects considered, describe all possible but realistic inter-attribute dependencies, and also include data quality attributes.
Discussion on Service Quality Metamodels
Here, the evaluation results are even better since most approaches include a rich constraint model. By closely inspecting the results of these three criteria, it can be concluded that pure SQMMs are constantly increasing their expressiveness, while the approaches of the other two divisions are more or less stable. The results show that most SQMMs have low complexity and that there is a tendency for pure SLA-enabled SQMMs to move towards higher complexity.
Also considering the fact that SLA-enabled SQMMs are increasing their expressivity in simple SLA-based aspects, this actually means that modelers are trying to increase the expressivity of their SQMMs and, as a result , the complexity of their SQMMs increases with respect to the number of concepts/entities. The first criterion assessed the association of an SQMM with a Service Functional Specification Language (SFSL) to assess whether the SQMM can be used in registries that are associated with particular SFSLs. The results showed that most SQMMs are associated with a SFSL.
By inspecting the functionality of existing frameworks that use pure SQMMs and considering the fact that these SQMMs do not model some critical information for service monitoring and assessment, it is deduced that pure SQMMs are used until the service negotiation activity. On the other hand, if the SLA-enabled SQMMs are improved on some modeling aspects, then they can be used across the entire service life cycle.
Discussion on Service-Level Agreement Metamodels
In addition, the capabilities of the WSLA and WS-Agreement languages are complementary in terms of supporting SLA management activities. InProceedings of the 2ndInternational Workshop on Service Oriented Engineering and Optimization (SENOPT'08) in collaboration with Conference on High Performance Computing.1–9. In Proceedings of the 4th Conference on USENIX Conference on Object-Oriented Technologies and Systems (COOTS.
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