An introduction to Graph Data Management

A graph database is a database where the data structures for the schema and/or instances are modeled as a (labeled)(directed) graph or generalizations of it, and where querying is expressed by graph-oriented operations and type constructors. In this article we present the basic notions of graph databases, give an historical overview of its main development, and study the main current systems that implement them

QBX: A CASE Tool for Data Mart Design

QBX is a CASE tool for data mart design resulting from a close collaboration between academy and industry. It supports designers during conceptual design, logical design, and deployment of ROLAP data marts in the form of star/snowflake schemata, and it can also be used by business users to interactively explore project-related knowledge at different levels of abstraction. We will demonstrate QBX functionalities focusing on both forward and reverse engineering scenarios

Data Warehouse Life-Cycle and Design

none1noThe term data warehouse life-cycle is used to indicate the phases (and their relationships) a data warehouse system goes through between when it is conceived and when it is no longer available for use. Apart from the type of software, life cycles typically include the following phases: requirement analysis, design (including modeling), construction, testing, deployment, operation, maintenance, and retirement. On the other hand, different life cycles differ in the relevance and priority with which the phases are carried out, which can vary according to the implementation constraints (i.e., economic constraints, time constraints, etc.) and the software specificities and complexity. In particular, the specificities in the data warehouse life-cycle derive from the presence of the operational database that feeds the system and by the extent of this kind of system that must be considered in order to keep the cost and the complexity of the project under control. Although the design phase is only a step within the overall life cycle, the identification of a proper life-cycle model and the adoption of a correct design methodology are strictly related since each one influences the other.mixedGolfarelli, MatteoGolfarelli, Matte

Containment of partially specified tree-pattern queries in the presence of dimension graphs

Nowadays, huge volumes of data are organized or exported in tree-structured form. Querying capabilities are provided through tree-pattern queries. The need for querying tree-structured data sources when their structure is not fully known, and the need to integrate multiple data sources with different tree structures have driven, recently, the suggestion of query languages that relax the complete speci?cation of a tree pattern

Heuristic approaches for checking containment of generalized tree-pattern queries

Query processing techniques for XML data have focused mainly on tree-pattern queries (TPQs). However, the need for querying XML data sources whose structure is very complex or not fully known to the user, and the need to integrate multiple XML data sources with different structures have driven, recently, the suggestion of query languages that relax the complete specification of a tree pattern. In order to implement the processing of such languages in current DBMSs, their containment problem has to be efficiently solved. In this paper, we consider a query language which generalizes TPQs by allowing the partial specification of a tree pattern. Partial tree-pattern queries (PTPQs) constitute a large fragment of XPath that flexibly permits the specification of a broad range of queries from keyword queries without structure, to queries with partial specification of the structure, to complete TPQs. We address the containment problem for PTPQs. This problem becomes more complex in the context of PTPQs because the partial specification of the structure allows new, non-trivial, structural expressions to be inferred from those explicitly specified in a query. We show that the containent problem cannot be characterized by homomorphisms between PTPQs, even when PTPQs are put in a canonical form that comprises all derived structural expressions. We provide necessary and sufficient conditions for this problem in terms of homomorphisms between PTPQs and (a possibly exponential number of) TPQs. To cope with the high complexity of PTPQ containment, we suggest a heuristic approach for this problem that trades accuracy for speed. An extensive experimental evaluation of our heuristic shows that our heuristic approach can be efficiently implemented in a query optimizer