Mahdi Abdelguerfi

Design strategies to improve performance of GIS Web services

GIS systems are ubiquitous distributed systems, since geo-spatial information adheres to almost everything. Considering the characteristics of GIS, the following four design-decision issues are particularly crucial: transactional mode (synchronous versus asynchronous), service granularity (finegrained versus coarse-grained), delivery manner (chunk versus stream), and transmission formats (GML versus binary). We have shared our experience in making choices in these four dimensions.

The 2-3TR-tree, a trajectory-oriented index structure for fully evolving valid-time spatio-temporal datasets

Supporting large volumes of multi-dimensional data is an inherent characteristic of modern database applications, such as Geographical Information Systems (GIS), Computer Aided design (CAD), and Image and Multimedia Databases. Such databases need underlying systems with extended features like query languages, data models, and indexing methods, as compared to traditional databases, mainly because of the complexity of representing and retrieving data. The presented work deals with access methods for databases that accurately model the real world. More precisely, the focus is on index structures that can capture the time varying nature of moving objects, namely spatio-temporal structures. A new taxonomy to classify these structures has been defined according to dataset characteristics and query requirements. Then, a new spatio-temporal access method, the 2-3TR-tree, has been designed to process specific datasets and fulfill specific query requirements that no other existing spatio-temporal index could handle.

Web Services for Geographic Information Systems

A surge in Web services and applications for geographic information systems (GISs) has made large spatial-data archives available over the Internet. Significant accomplishments in GIS Web services have led to several exemplifying map and image services that adhere to Web services standards and provide geospatial data and digital maps to enterprise developers.

Stream data management

to Stream Data Management.- Query Execution and Optimization.- Filtering, Punctuation, Windows and Synopses.- XML & Data Streams.- CAPE: A Constraint-Aware Adaptive Stream Processing Engine.- Efficient Support for Time Series Queries in Data Stream Management Systems.- Managing Distributed Geographical Data Streams with the GIDB Portal System.- Streaming Data Dissemination Using Peer-Peer Systems.

Representation of 3-D elevation in terrain databases using hierarchical triangulated irregular networks: a comparative analysis

3-D terrain representation plays an important role in a number of terrain database applications. Hierarchical Triangulated Irregular Networks (TINs) provide a variable-resolution terrain representation that is based on a nested triangulation of the terrain. This paper compares and analyzes existing hierarchical triangulation techniques. The comparative analysis takes into account how aesthetically appealing and accurate the resulting terrain representation is. Parameters, such as adjacency, slivers, and streaks, are used to provide a measure on how aesthetically appealing the terrain representation is. Slivers occur when the triangulation produces thin and slivery triangles. Streaks appear when there are too many triangulations done at a given vertex. Simple mathematical expressions are derived for these parameters, thereby providing a fairer and a more easily duplicated comparison. In addition to meeting the adjacency requirement, an aesthetically pleasant hierarchical TINs generation algorithm is expect...

A Shell-Neutral Modeling Approach Yields Sustainable Oyster Harvest Estimates: A Retrospective Analysis of the Louisiana State Primary Seed Grounds

ABSTRACT A numerical model is presented that defines a sustainability criterion as no net loss of shell, and calculates a sustainable harvest of seed (<75 mm) and sack or market oysters (≥75 mm). Stock assessments of the Primary State Seed Grounds conducted east of the Mississippi from 2009 to 2011 show a general trend toward decreasing abundance of sack and seed oysters. Retrospective simulations provide estimates of annual sustainable harvests. Comparisons of simulated sustainable harvests with actual harvests show a trend toward unsustainable harvests toward the end of the time series. Stock assessments combined with shell-neutral models can be used to estimate sustainable harvest and manage cultch through shell planting when actual harvest exceeds sustainable harvest. For exclusive restoration efforts (no fishing allowed), the model provides a metric for restoration success—namely, shell accretion. Oyster fisheries that remove shell versus reef restorations that promote shell accretion, although divergent in their goals, are convergent in their management; both require vigilant attention to shell budgets.

Hardware Implementation of Relational Algebra Operations

The relational database model introduced by Codd in [1, 2, 3, 4, 5] has received considerable attention during the last several years. There is an increasing recognition of the relational data model’s advantages of simplicity, symmetry of access, and data independence. Another feature of the relational model is that the database may be manipulated by high level, non-procedural data manipulation languages [6,7]. Perhaps the most important feature of the relational database model is that it is based on strong theoretical foundations [8]. This allows for an efficient design of database schemas. In general this is acheived using the normalization theory [5, 9].

Achieving interoperability for integration of heterogeneous COTS geographic information systems

Using multiple commercial off-the-shelf (COTS) GIS suites is a common phenomenon, because different COTS products often have different strengths in various applications. On the other hand, deploying heterogeneous GIS software has the tendency to form fragmented data sets and to cause inconsistency. Data consolidation is an effective way to preserve data integrity. To accomplish this, we must achieve interoperability between different GIS tools. While vector spatial data have the standard database models to support interoperability, raster based images have been conventionally managed as files. Compared to the database approach, the file-based management for raster data is disadvantageous in terms of performance and flexibility. We implemented an adapter that allowed the file-based GIS tools to access the raster data storage in databases managed by a COTS software product. To integrate the COTS GIS into the Java 2 Platform Enterprise Edition (J2EE) framework, we have further enhanced this adapter and made it compliant to the J2EE Connector Architecture (J2EE-CA) standard. Using this kind of J2EE-CA adapter, any GIS can be managed by any J2EE server. The J2EE framework is an ideal foundation for building enterprise-wide geographic information systems.

Efficient AKNN spatial network queries using the M-Tree

Aggregate K Nearest Neighbor (AKNN) queries are problematic when performed within spatial networks. While simpler network queries may be solved by a single network traversal search, the AKNN requires a large number costly network distance computations to completely compute results. The M-Tree index, when used with Road Network Embedding, provides an efficient alternative which can return estimates of the AKNN results. The M-Tree index can then be used as a filter for AKNN results by quickly computing a superset of the query results. The final AKNN query results can be computed by sorting the results from the M-Tree. In comparison to Incremental Euclidean Restriction (IER), the M-Tree reduces the overall query processing time and the total number of necessary network distance computations required to complete a query. In addition, the M-Tree filtering method is tunable to allow increasing performance at the expense of accuracy, making it suitable for a wide variety of applications.

Computational complexity of sorting and joining relations with duplicates

It is shown that the existence of duplicate values in some attribute columns has a significant impact on the computational complexity of the sorting and joining operations. This is especially true when the number of distinct tuple values is a small fraction of the total number of tuples. The authors characterize a multirelation M(n, L) by its cardinality n and the number of distinct elements L it contains. Under this characterization, the worst time complexity of sorting such a multirelation with binary comparisons as basic operations is investigated. Upper and lower bounds on the number of three-branch comparisons needed to sort such a multirelation are established. Thereafter, the methodology used to study the complexity of sorting is applied to the natural join operation. It is shown that the existence of duplicate values in the join attribute columns can be exploited to reduce the computational complexity of the natural join operation. >