We study a security model for searching documents containing each of several keywords (conjunctive keyword search) over encrypted documents. A conjunctive keyword search protocol consists of three entities: a data supplier, a storage system such as database, and a user of storage system. A data supplier uploads encrypted documents on a storage system, and then a user of the storage system searc...

When answering queries using external information sources, their contents can be described by views. To answer a query, we must rewrite it using the set of views presented by the sources. When the external information sources also have the ability to answer some (perhaps limited) sets of queries that require performing operations on their data, the set of views presented by the source may be in...

A conjunctive query problem is a problem to determine whether or not a tuple belongs to the answer of a conjunctive query over a database. Here, a tuple, a conjunctive query and a database in relational database theory are regarded as a ground atom, a nonrecursive function-free definite clause and a finite set of ground atoms, respectively, in inductive logic programming terminology. An acyclic...

Rural Development is a priority in Europe and it is supported by specific, financial programmes. At the same time, sustainability is the key word for the European Union to construct programmes and policies for all human activities. However, measuring sustainability of rural areas is not easy, due to their particular features. The improvement of knowledge on sustainability in rural areas is impo...