This paper presents the system architecture of a Content- Based Image Retrieval system implemented as a web service. The proposed solution is composed of two parts, a client run- ning a graphical user interface for query formulation and a server where the search engine explores an image repository. The separation of the user interface and the search engine follows a Service as a Software (SaaS) model, a type of cloud computing design where a single core system is online and available to authorized clients. The proposed architecture follows the REST software architecture and HTTP proto- col for communications, two solutions that combined with metadata coded in RDF, make the proposed system ready for its integration in the semantic web. User queries are formulated by visual examples through a graphical inter- face and content is remotely accessed also through HTTP communication. Visual descriptors and similarity measures implemented in this work are mostly de ned in the MPEG-7 standard, while textual metadata is coded according to the Dublin Core speci cations.

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