Semantic query optimization is an important issue in many contexts of databases including information integration, view maintenance and data warehousing and can substantially improve performance, especially in today's database systems which contain gigabytes of data. A crucial issue in semantic query optimization is query containment. Several papers have dealt with the problem of conjunctive query containment. In particular, some of the literature admits SQL like query languages with aggregate operations such as sum/count. Moreover, since real SQL requires a richer semantics than set semantics, there has been work on bag-semantics for SQL, essentially by introducing an interpreted column. One important technique for reasoning about query containment in the context of bag semantics is to translate the queries to alternatives using aggregate functions and assuming set semantics. Furthermore, in SQL, order by is the operator by which the results are sorted based on certain attributes and, clearly, ordering is an important issue in query optimization. As such, there has been work done in support of ordering based on the application of the domain. However, a final step is required in order to introduce a rich semantics in support. In this work, we integrate set and bag semantics to be able to reason about real SQL queries. We demonstrate an ordered bag semantics for SQL using a relational algebra with aggregates. We define a set algebra with various expressions of interest, then define syntax and semantics for bag algebra, and finally extend these definitions to ordered bags. This is done by adding a pair of additional interpreted columns to computed relations in which the first column is used in the standard fashion to capture duplicate tuples in query results, and the second adds an ordering priority to the output. We show that the relational algebra with aggregates can be used to compute these interpreted columns with sufficient flexibility to work as a semantics for standard SQL queries, which are allowed to include order by and duplicate preserving select clauses. The reduction of a workable ordered bag semantics for SQL to the relational algebra with aggregates - as we have developed it - can enable existing query containment theory to be applied in practical query containment.

Semantic query optimization is an important issue in many contexts of databases including information integration, view maintenance and data warehousing and can substantially improve performance, especially in today's database systems which contain gigabytes of data. A crucial issue in semantic query optimization is query containment. Several papers have dealt with the problem of conjunctive query containment. In particular, some of the literature admits SQL like query languages with aggregate operations such as sum/count. Moreover, since real SQL requires a richer semantics than set semantics, there has been work on bag-semantics for SQL, essentially by introducing an interpreted column. One important technique for reasoning about query containment in the context of bag semantics is to translate the queries to alternatives using aggregate functions and assuming set semantics. Furthermore, in SQL, order by is the operator by which the results are sorted based on certain attributes and, clearly, ordering is an important issue in query optimization. As such, there has been work done in support of ordering based on the application of the domain. However, a final step is required in order to introduce a rich semantics in support. In this work, we integrate set and bag semantics to be able to reason about real SQL queries. We demonstrate an ordered bag semantics for SQL using a relational algebra with aggregates. We define a set algebra with various expressions of interest, then define syntax and semantics for bag algebra, and finally extend these definitions to ordered bags. This is done by adding a pair of additional interpreted columns to computed relations in which the first column is used in the standard fashion to capture duplicate tuples in query results, and the second adds an ordering priority to the output. We show that the relational algebra with aggregates can be used to compute these interpreted columns with sufficient flexibility to work as a semantics for standard SQL queries, which are allowed to include order by and duplicate preserving select clauses. The reduction of a workable ordered bag semantics for SQL to the relational algebra with aggregates - as we have developed it - can enable existing query containment theory to be applied in practical query containment.

Este trabalho apresenta o desenvolvimento de um Framework de persistência que utiliza banco de dados objeto-relacional como mecanismo de persistência. Tendo por objetivo usar os conceitos de orientação a objetos descritos na norma SQL:2008, conceitos como: objeto (atributos e métodos), herança, agregação, composição, referências (REF) e estruturas multivaloradas (arrays e multiset). Para tanto se desenvolveu e formalizou (XSD) um arquivo XML que representa um esquema de objetos através da norma SQL:2008. Da mesma forma definiu-se um conjunto de anotações Java, com o intuito de facilitar a utilização e configuração do Framework, o qual é chamado de O-ODBM (Object Object-Relational Database Management). / Persistent Frameworks have been used to aid developers, managing all access to DBMS. This kind of tool maps objects from OO applications to relational databases. Besides, allow developers to persist objects without solid knowledge about DBMSs and specific languages, making better the developers productivity, mainly when different DBMS is used. On the other hands, since 1999 the SQL specification has introduced new features to manipulate objects in relational databases which since then has been called Object-Relational Database (ORDB). At present, many DBMS offer resources to manipulate objects in database, but the most of the application developers just map class to relations tables, failing to exploit the strength of O-R model. The lack of the tools that aid the project of database contributes to this situation. Considering the vantages of use of the persistent frameworks and the ORDBs, this article introduces the O-ODM (Object-Object Database Mapping) a persistent framework for relational object databases.

Este trabalho apresenta o desenvolvimento de um Framework de persistência que utiliza banco de dados objeto-relacional como mecanismo de persistência. Tendo por objetivo usar os conceitos de orientação a objetos descritos na norma SQL:2008, conceitos como: objeto (atributos e métodos), herança, agregação, composição, referências (REF) e estruturas multivaloradas (arrays e multiset). Para tanto se desenvolveu e formalizou (XSD) um arquivo XML que representa um esquema de objetos através da norma SQL:2008. Da mesma forma definiu-se um conjunto de anotações Java, com o intuito de facilitar a utilização e configuração do Framework, o qual é chamado de O-ODBM (Object Object-Relational Database Management). / Persistent Frameworks have been used to aid developers, managing all access to DBMS. This kind of tool maps objects from OO applications to relational databases. Besides, allow developers to persist objects without solid knowledge about DBMSs and specific languages, making better the developers productivity, mainly when different DBMS is used. On the other hands, since 1999 the SQL specification has introduced new features to manipulate objects in relational databases which since then has been called Object-Relational Database (ORDB). At present, many DBMS offer resources to manipulate objects in database, but the most of the application developers just map class to relations tables, failing to exploit the strength of O-R model. The lack of the tools that aid the project of database contributes to this situation. Considering the vantages of use of the persistent frameworks and the ORDBs, this article introduces the O-ODM (Object-Object Database Mapping) a persistent framework for relational object databases.