José de Aguiar Moraes Filho

Sharing mobile databases in dynamically configurable environments

In an environment with support for mobile computing, we may have a collection of autonomous, distributed, heterogeneous and mobile databases, denoted Mobile Database Community (MDBC), in which each database user can access databases in the community through a wireless communication infrastructure. In such an environment, new participants may join to an MDBC as they move within communication range of one or more hosts which are members of the MDBC. Furthermore, MDBC participants may transiently disconnect from the network due to communication disruptions or to save power. Therefore, an MDBC can be characterized as a dynamically configurable environment. This paper describes an agent-based architecture, denoted AMDB (Accessing Mobile Databases), which enables such communities to be formed opportunistically over mobile database hosts in ad hoc configurable environments. The AMDB architecture is fully distributed and has the capability of exploiting physical mobility of hosts and logical mobility of database queries and their results across mobile hosts.

EXsum: an XML summarization framework

We propose a new framework for the summarization of XML document properties called EXsum (Element-wise XML summarization), which can capture statistical information of all important XPath axes related to (the nodes having) the same element name in a document. Compared to conventional summaries, cardinality estimates for a richer spectrum of XPath/XQuery expressions can be provided for query optimization. For the important class of queries consisting of one or two location steps only, even accurate cardinalities are computed. Besides adequate storage consumption, it provides fast access times which helps to keep the query optimization overhead low. Using a collection of XML documents embodying considerable structural variations, we have empirically analyzed the EXsum framework by running a large number of experiments in our XML native database management system called XTC. These evaluations clearly show the predominance of EXsum as to important aspects when compared to competitor approaches.

On mobile transaction processing in dynamically configurable mobile database communities

The topology of a mobile ad hoc network (MANET) may change randomly and rapidly at an unpredictable time, since nodes are free to move arbitrarily. In such an environment, we may have a collection of autonomous, distributed, heterogeneous and mobile databases (denoted mobile database community (MDBC)). This paper describes an approach for controlling concurrency of mobile transactions executed in MDBCs. The proposed approach is based on the use of semantic knowledge to relax the notion of absolute transaction atomicity. Supported by this new concept of atomicity, we propose a new correctness criterion, denoted mobile semantic serializability, for the execution of concurrent transactions in MDBCs. The proposed correctness criterion provides a high degree of inter-transaction parallelism and ensures consistency of the mobile database.

Increasing mobile transaction concurrency in dynamically configurable environments

The topology of a mobile ad hoc network (MANET) may change randomly and rapidly at unpredictable time, since nodes are free to move arbitrarily. In such an environment, we may have a collection of autonomous, distributed, heterogeneous and mobile databases (denoted mobile database community or MDBC). This paper describes an approach for controlling concurrency of mobile transactions executed in MDBCs. The proposed approach is based on the use of semantic knowledge to relax the notion of absolute transaction atomicity. Supported by this new concept of atomicity, we propose a new correctness criterion, denoted mobile semantic serializability, for the execution of concurrent transactions in MDBCs. The proposed correctness criterion provides a high degree of inter-transaction parallelism and ensures consistency of the mobile database.

Enhanced Statistics for Element-Centered XML Summaries

Element-centered XML summaries collect statistical information for document nodes and their axes relationships and aggregate them separately for each distinct element/attribute name. They have already partially proven their superiority in quality, space consumption, and evaluation performance. This kind of inversion seems to have more service capability than conventional approaches. Therefore, we refined and extended element-centered XML summaries to capture more statistical information and propose new estimation methods. We tested our ideas on a set of documents with largely varying characteristics.

Accurate histogram-based XML summarization

In this paper, we propose the use of histograms to characterize node set distributions in an XML document, which then can be recursively evaluated for query optimization tasks. We identify and deal with special cases for effectively using histograms to summarize structural aspects of XML documents. To reveal the potential of our approach, we perform comparative experiments on our native XML database management system called XTC.

DaC scan: a novel scan operator for exploiting SSD internal parallelism.

Solid‐state drives (SSDs) have become an attractive alternative for storing large databases. Solid‐state drives do not present mechanical parts in their assembly. Consequently, SSDs have different characteristics and capabilities than magnetic disks Hard Disk Drives (HDDs). One of the most important features of SSDs is the fact that they implement different levels of internal parallelism for executing read/write operations. In database query processing, the table scan operator is responsible for reading an entire table. Generally, a scan operator is utilized whenever there is no index defined on the table to be accessed. This paper introduces a novel scan operator, denoted DaC Scan, for reading database tables stored in SSDs. The key goal of the proposed operator is to explore IO parallelism. Thus, the idea is to make DaC Scan able to read different regions of a single table simultaneously. For validation of DaC Scan efficiency, experiments with a prototype have been conducted over the TPC‐H benchmark database, scale factors 10 and 20. The results show that DaC Scan is efficient, presenting significant gains w.r.t. classical scan operators.

Bt-Join: a join operator for asymmetric storage device

Nowadays the use of solid state drives (SSDs) is a reality for storing large databases. SSDs are capable to provide IOPS rates up to three orders of magnitude greater than the rates delivered by hard disk drives (HDD). Nonetheless, SSDs presents time asymmetry for executing read/write operations, which poses challenges on the database technology. This is because existing database management systems (DBMS) have been designed by assuming that databases are stored on devices, in which read/write operations are executed in the same amount of time. Thus, we claim that to take full profit from SSD properties, components of DBMS should be aware of read/write asymmetry in SSDs. It is well known that the join operation is the query operator which requires the highest amount of accesses (read/write operations) to the secondary memory. In this paper, we present a new join algorithm, called Bt-Join. The key goal of Bt-Join is to reduce the amount of write operations during the execution of any join operation R ⋈ S. We have empirically evaluated Bt-Join. The results show that the proposed join operator can be up to 50% faster than FlashJoin, a well-known join operator proposed to be deployed in SSDs.