In an article Design of a Service-Oriented Architecture for a Federated Systems, Daniel Calegari, Marcos Viera, and Regina Motz (2005) proposed a Service-Oriented Architecture to be applied in Federal Systems. Federated Systems are composed of computer systems or databases that are independent, cooperative, heterogeneous, and autonomous used in data sharing. Service-Oriented Architecture, on the other hand, has functions which provide independent services and transparent communication.
The application of this type of architecture will provide practical services for Federated Systems such as allowing data sharing of many users, access control and rights to data, integration and querying processes with high level of automation, determining the foundations if the federation’s management framework, and validating both the framework and the architecture (Calegari et al. , 2005, p. 167).
A Federated System has three properties: (1) distribution, which allows for data distribution logically and physically; (2) autonomy, which allows independent execution and user access to data; and, (3) heterogeneity, which can provides heterogeneity on sources’ execution, semantics, structure, and query language. The proposed design for a Federated System by Calegari et al. (2005) is consist of five-level architecture including the properties mentioned.
Every source will have a local schema (and a query language each) that will be converted to a schema with canonical language using the transforming processor to produce a component schema. The access control of the federation to the information id is determined by each source through a filtering processor that will be generating an export schema to each source. Through a constructing processor, a federated schema will be produced. In order for the users to access the data, the filtering processor will execute another access control that will generate an external schema for the user’s access (Calegari et al. 2005, p. 167)..
The properties of a Service-Oriented Architecture allow for the heterogeneity and reusability of a framework and if this will be applied in Federated Systems, users’ access to data will be more convenient. In order to validate the performance of the proposed architecture, Calegari et al. (2005) has developed a prototype equipped with architecture structure for the federation such as federation controller, integrator, query decomposer, invoker, and rights manager (p. 69); and also structure for the source such as service controller, query filter, schema filter, data source connector, and rights manager (p. 170).
Each of the sources will be providing a schema, permissions for profile exportation, and CRUD operations in order for the federation to offer administrative and federation functionalities. One of the significant features of the proposed architecture is the automation of the selected processes. The achievability of the functional system based from the proposed architecture has been demonstrated in the prototype (Calegari et al. 2005, p. 171).
The proposed design using a five-level Service-Oriented Structure maintains the properties of sources in Federated Systems and also supports user profiles, access rights for data, and transparency. Databases are incorporated, abstract applications are used applied for the users, automation of components are tested and analyzed, and the bases for the management framework of federation are determined. There have been various studies on the application of Service-Oriented Architectures but none has dealt with the complexities of the integration and querying processes.
However, the prototype that Calegari et al. (2005) created is not yet a completely functional version. In the end of the article, they listed the future works that must be done to achieve a functional version such as generation of a multi-language framework; integration of improved management tools; advancement to new strategies with access rights supports by using concrete schema integration and validation strategies for query decomposition such as SIM; and, study of other schema formats and query languages as alternatives (Calegari et al. , 2005, p. 172).. Review
In a Federated System, unlike in the Integrated System, is much preferred since it major functions are equipped with computer systems providing many application functions (Obermaisser 2005). However, Federated Systems encounter a number of problems relating to its structure, semantics, and its independent database systems which require constant modifications (Dogac 1994). There are other complex constraints of federated systems and perhaps the popularity and usability of Service-Oriented Architecture (SOA) in many enterprises became an inspiration for Calegari et al. 2005) to propose a service-oriented architecture design for federated systems.
IBM refers to service-oriented architecture as a “business-centric IT architectural approach that supports integrating business as linked, repeatable business tasks, or services” ("Service-Oriented Architecture," 2008). Also the World Wide Web Consortium (W3C) described SOA as “a set of components which can be invoked, and whose interface descriptions can be published and discovered”.
Service-oriented architecture considers services both in technological perspective and in normalizing the service-oriented environment (Blecker, 2007, p. 145). The goal of Calegari et al. (2005) to design a SOA for a flexible functionality of Federated Systems might as well be successful. According from Blecker and Friedrich (2007), SOA offers services’ description, publication, registration, and search functionalities. The services and standardized mechanisms are combined in order to achieve a “dynamic and universal service discovery and execution” (p. 45).
In case study sample in Design of a Service-Oriented Architecture for a Federated Systems which is the Medical Federation, Calegari et al. (2005) are able to demonstrate the significance of the SOA in the integration and querying processes. Additionally, application of SOA, combined with other technologies particularly the web services, can simplify the system design and business implementation with a framework that is more practical and extensively used in outsourcing processes (Siau, 2003, p. 290). Calegari et al. 2005) have provided an extensive explanation and descriptions on the desired capabilities of the SOA design proposed for Federated Systems.
Descriptions on the export schema and filtering process are provided in order to sustain the desired capabilities. SOA had been used in many enterprises and fields and this study has even provided wide possibilities for developing the querying and integration processes that have not been highly focused by other related works particularly by Alvarez and Amador in June 2005.