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The number of Web services has grown drastically. Then how to manage them efficiently in a service repository is an important issue to address. Given a special field, there often exists an efficient data structure for a class of objects, e.g., the Google' Bigtable is very suitable for Web pages' storage and management. Based on the theory of the equivalence relations and quotient sets, this work proposes a multilevel index model for large-scale service repositories, which can be used to reduce the execution time of service discovery and composition. Its novel use of keys as inspired by the key in relational database can effectively remove the redundancy of the commonly-used inverted index. Its four function-based operations are for the first time proposed to manage and maintain services in a repository. The experiments validate that the proposed model is more efficient than the existing structures, i.e., sequential and inverted index ones.
When these services are stored in a repository, they can lower service composition and discovery efficiencies. there are many similar tourinfo-lookup services and car-rent ones, it is very possible to retreive more than what users need to complete the composition. If services with the same input and output parameters are clustered into a class and formed a virtual service, the search space can be reduced.
This method is simple but effective for these service sets that cantain many similar services. After the clustering, a new service can be composed in the level of virtul services. When the composed workflow is completed, a real service need to be binded. How to select a desirable serivce from many similar ones is another research field called service selection.
In order to eliminate the redundancy residing in the inverted index, this work proposes two new level indexes. Keys are used in tables of relational databases to reduce some redundancies, which is similar to the redundancy residing in the inverted index. Inspired by this, a new concept of a key for the input parameters is proposed.
A question is how to determine the keys of input-similar classes. Their determination is not the task of a service designer but the multilevel index modeler. They can be determined by the cardinality of Ck, denoted as |Ck|, in the proposed model automatically.
Different methods to improve the service composition efficiency. Their common shortcoming is that they are considered to be parts of their composition methods but not independent systems. Therefore, they are not considered as the support for service discovery, management and maintenance, e.g., service addition and deletion. However, as the number of services increases, the demand becomes more and more intense for an independent system that can provide great support for not only service composition but also discovery and be conveniently managed and maintained.
Tree-based search algorithm for Web service composition in a cloud computing platform. They first create a tree that represents all possible composition solutions according to user requirements, and then prune the illegal branches aiming to reduce response time and improve performance, and finally use a heuristic algorithm to search an optimal solution. This method has the disadvantage similar to that in, namely, its optimization process cannot be executed before receiving user requirements.
The proposed model contains four level indexes. The first two are constructed according to inputs and outputs of services and are easy to understand. The last two are constructed according to a newly introduced concept called "Key", and can successfully remove redundancy contained in the inverted index SPACE.
The contributions of this work are summarized as follows:
1. Based on the theory of the equivalence relations and quotient sets, this work proposes a multilevel index model for service repositories, which can reduce the service discovery and composition time to the extent never possible by using existing methods.
2. Based on functions implied in the proposed multilevel index model, this work proposes four operations that can retrieve, insert, delete and replace services easily.
3. The experiments validate that the proposed multilevel index is more efficient than the other two best structures in literatures.
This work proposes a multilevel index model to store and manage services for large-scale service repositories. Based on the theory of the equivalence relations and quotient sets, four level indexes are given to construct the multilevel index model. Four operations are proposed to manage and maintain services based on functions implied in the proposed model. The theoretical analysis and experimental results validate that the proposed multilevel index is more efficient and stable for service discovery and composition than the sequential structure and inverted index. Especially, the advantages of the proposed model become clearer and more significant as the number of service increases.
Our experiments validate that our four operations are efficient. In the era of drastically expanding services, the proposed model provides a highly desired storage structure for large-scale service repositories. The proposed model, such as how many input parameters each service has, how many services contain the same parameter as an input one, and the probability of each service is invoked. It requires more in-depth and systematic studies. Accordingly, how to adjust addition operation according to different cases with different factors in order to keep high efficiency of the proposed model needs to be studied.