Modeling and Simulating Federated Databases for early Validation of Federated Searches using the Broker-based SysML Toolbox

In research and cultural institutions as well as in companies, many data are collected and increasingly stored in databases. For example, during the project EDAK (Epigraphische Datenbank zum antiken Kleinasien) the Department for Ancient History at the Universität Hamburg created an epigraphic database of ancient Asia Minor. This database contains a collection of Greek and Latin inscriptions from modern-day Turkey. For analyzing data, a user usually sends a query to one database and receives an answer. However, it is not always sufficient to use one database only. For example, the fragment AO 29196 is located at the Louvre. The counterpart of this fragment is the fragment KUG 15 which is located in Germany. Indeed, both fragments were found without database federation, but in the future, for analyzing data from different databases it would be desirable to find related data in a FDBS. This example highlights the need to sometimes combine, analyze, and query data from different databases. Database federation offers a logical centralization of data without the need to change physical implementation of the databases. Thus, the complexity of query execution increases. Users send queries to the FDBS, and then the FDBS forwards queries to each (relevant) database node. The answer to queries vary. The response may be correct, incorrect, or incomplete. To overcome this problem, theoretical foundations have been developed. Although theories exist for implementing FDBSs, in practice, the implementation of a FDBS is a complex task. When using the currently-existing FDBS such as Denodo, a programmer or engineer still has to develop a congruent overview for querying internal as well as external databases. An FDBS is often expensive to develop. We predict that early validation of federated searches may identify problems which need to be solved before implementation. Therefore, we recommend carrying out a feasibility study before a FDBS is set up. In this paper we present how to model and simulate federated databases before implementation. The development of database federation for early validation of federated searches is challenging due to the distribution, heterogeneity, and autonomy. In order to support the development, established methods, tools, and languages for modeling, simulating, and validating systems are useful. Developers are supported in model-based development using the SysML, the modeling and simulation tool Cameo Systems Modeler and the broker-based SysML Toolbox. For modeling and simulation, we use the tool Cameo Systems Modeler and the broker-based SysML Toolbox. In addition, we evaluate our model-based approach by feasibility study by means of a prototypical implementation of federated databases. This paper is structured as follows. First, the databases are briefly described which are used for the feasibility study. Second, the broker-based SysML Toolbox, as an extension of the tool Cameo Systems Modeler, is introduced which contributes in creating communications networks. Third, broker federation is explained, followed by describing the characteristics of federated databases and the challenges providing federated searches. Subsequently the model-based approach for modeling and simulating an FDBS with low coding efforts is demonstrated. Afterwards an evaluation for federated searches is presented. Finally, a short conclusion is given.