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--- teaching:mfe:is [2016/02/16 10:26]
svsummer [Engineering a runtime system and compiler for AQL]
+++ teaching:mfe:is [2019/06/07 15:12]
svsummer [Multi-query Optimization in Spark]
@@ Line 1: / Line 1: @@
-====== MFE 2015-2016 : Web and Information Systems ======
+====== MFE 2019-2020 : Web and Information Systems ======
 ===== Introduction =====
@@ Line 18: / Line 18: @@
 ===== Master Thesis in Collaboration with Euranova =====
-Our laboratory performs collaborative research with Euranova R&D (http://euranova.eu/). The list of subjects proposed for this year by Euranova can be found
+Our laboratory performs collaborative research with Euranova R&D (http://euranova.eu/). The list of subjects proposed for this year by Euranova can be found [[https://research.euranova.eu/wp-content/uploads/proposals-thesis-2019.pdf|here]].
-{{:teaching:mfe:master_thesis_euranova_2015.pdf|here}}
 These subject include topics on distributed graph processing, processing big data using Map/Reduce, cloud computing, and social networks.
@@ Line 26: / Line 26: @@
-===== Graph Indexing for Fast Subgraph Isomorphism Testing =====
-There is an increasing amount of scientific data, mostly from the bio-medical sciences, that can be represented as collections of graphs (chemical molecules, gene interaction networks, ...). A crucial operation when searching in this data is that of subgraph    isomorphism testing: given a pattern P that one is interested in (also a graph) in and a collection D of graphs (e.g., chemical molecules), find all graphs in G that have P as a   subgraph. Unfortunately, the subgraph isomorphism problem is computationally intractable. In ongoing research, to enable tractable processing of this problem, we aim to reduce the number of candidate graphs in D to which a subgraph isomorphism test needs   to be executed. Specifically, we index the graphs in the collection D by means of decomposing them into graphs for which subgraph   isomorphism *is* tractable. An associated algorithm that filters graphs that certainly cannot match P can then formulated based on ideas from information retrieval.
-In this master thesis project, the student will emperically validate on real-world datasets the extent to which graphs can be decomposed into graphs for which subgraph isomorphism is tractable, and run experiments to validate the effectiveness of the proposed method in terms of filtering power.
+===== Dynamic Query Processing in Modern Big Data Architectures =====
-**Interested?** Contact : [[stijn.vansummeren@ulb.ac.be|Stijn Vansummeren]]
+Dynamic Query Processing refers to the activity of processing queries under constant data updates. (This is also known as continuous querying). It is a core problem in modern analytic workloads.
-**Status**: available
+Modern big data compute architectures such as Apache Spark, Apache Flink, and apache Storm support certain form of Dynamic Query Processing.
+In addition, our lab has recently proposed DYN, a new Dynamic Query Processing algorithm that has strong optimality guarantees, but works in a centralised setting.
-=====  Complex Event Processing for Security Analytics=====
+The objective of this master thesis is to propose extensions to our algorithm that make it suitable for distributed implementation on one of the above-mentioned platforms, and compare its execution efficiency against the state-of-the art solutions provided by Spark, Flink, and Storm. In order to make this comparison meaningfull, the student is expected to research, survey, and summarize the principles underlying the current state-of-the art approaches.
-As noted by [[http://home.deib.polimi.it/cugola/Papers/cep_survey.pdf|Cugola and Magara]], "an increasing number of distributed applications requires processing continuously flowing data ("events") from geographically distributed sources at unpredictable rates to obtain timely responses to complex queries. Examples of such applications come from the most disparate fields: from fraud  detection to network intrusion detection systems, from wireless sensor networks to financial tickers, from traffic management to click-stream inspection."
+**Deliverables** of the master thesis project
+     * An overview of the continuous query processing models of Flink, Spark and Storm
+     * A qualitive comparison of the algorithms used
+     * A proposal for generalizing DYN to the distributed setting.
+     * An implementation of this geneneralization by means of a compiler that outputs a continous query processing plan
+     * A benchmark set of continuous queries and associated data sets for the experimental validation
+     * An experimental validation of the extension and state of the art
-These requirements have led to the development of a number of systems specifically designed to process information as a flow (or a set of flows) of continues data "events" according to a set of pre-deployed processing rules.  Despite having a common goal, these systems differ in a wide range of aspects, including architecture, data models, rule and pattern languages, and processing mechanisms. In part, this is due to the fact that they were the result of the research efforts of different communities, each one bringing its own view of the problem and its background to the definition of a solution.
-The master thesis is put forward in the context of the SPICES "Scalable Processing and mIning of Complex Events for Security-analytics" research project, funded by Innoviris.
+**Interested?** Contact :  [[svsummer@ulb.ac.be|Stijn Vansummeren]]
-The objective of this master thesis is to survey the existing systems and compare the strengths and weaknesses when they are applied specifically to the context detecting security breaches (network intrusion, fraud detection, ...), and help, as part of the research project, in the design & implementation of a new system that overcomes these weaknesses.
-**Interested?** Contact : [[stijn.vansummeren@ulb.ac.be|Stijn Vansummeren]]
-**Status**: already taken.
-===== Compiling SPARQL queries into machine code =====
-Due to the increasing availability of larger and larger cheap RAM memories, the working set of modern database management systems becomes more and more main memory resident. This implies that, in contrast to traditional database management systems, slow disk accesses are rare, and that hence, the in-memory processing speed of databases becomes an important factor. As recently observed by a number of researchers, (e.g., [[http://sites.computer.org/debull/A14mar/p3.pdf|Neumann and Leis]]), one very attractive approach for fast query processing in this context is the just-in-time compilation of incoming queries into machine code. This compilation avoids the overhead of the traditional interpretation of query plans, and can aid in minimzing memory traffic for boosting performance.
-A number of recent research prototypes exist that compile SQL queries into machine code in this sense:  HyPer A Hybrid OLTP&OLAP High Performance DBMS (http://hyper-db.de/) and Legobase (https://github.com/epfldata/NewLegoBase and http://data.epfl.ch/legobase).
-The objective of this master thesis is to apply the same methodology to engineer a compiler that translates (fragments of) SPARQL (the standard query language for querying RDF data on the semantic web) into machine code. The overall methodology should follow the methodology used by HyPer and Legobase:
-  * Use of a high-level language to construct the compiler (Scala, http://scala-lang.org/)
-  * Use of Latent Modular Staging (LMS for short) for generating low-level portable assembly code at runtime (http://scala-lms.github.io/)
-  * Use of LLVM (http://llvm.org/) as a portable assembly code and corresponding translator to machine code.
-Getting aquaintend with these technologies is part of the master thesis objective.
-**Validation of the approach** The thesis should propose a benchmark collection of SPARQL queries that can be used to test the obtained SPARQL-to-machine-code compiler and compare its perforance against a reference, interpreter-based SPARQL compiler.
-**Deliverables** of the master thesis project:
-  - An overview of the state of the art in query-to-machine-code compilation.
-  - A description of latent modular staging and how it can be used to construct machine-code compilers.
-  - The SPARQL compiler (software artifact)
-  - A benchmark set of SPARQL queries and associated data sets for the experimental validation
-  - An experimental validation of the compiler, comparing efficiency of compiled queries against a reference compiler based on query plan interpretation.
-**Interested?** Contact : [[stijn.vansummeren@ulb.ac.be|Stijn Vansummeren]]
 **Status**: available
+===== Graph Indexing for Fast Subgraph Isomorphism Testing =====
-===== An implementation of the SCULPT schema language for tabular data on the Web =====
+There is an increasing amount of scientific data, mostly from the bio-medical sciences, that can be represented as collections of graphs (chemical molecules, gene interaction networks, ...). A crucial operation when searching in this data is that of subgraph    isomorphism testing: given a pattern P that one is interested in (also a graph) in and a collection D of graphs (e.g., chemical molecules), find all graphs in G that have P as a   subgraph. Unfortunately, the subgraph isomorphism problem is computationally intractable. In ongoing research, to enable tractable processing of this problem, we aim to reduce the number of candidate graphs in D to which a subgraph isomorphism test needs   to be executed. Specifically, we index the graphs in the collection D by means of decomposing them into graphs for which subgraph   isomorphism *is* tractable. An associated algorithm that filters graphs that certainly cannot match P can then formulated based on ideas from information retrieval.
-Despite the availability of numerous standardized formats for semi-structured and semantic web data such as XML, RDF, and JSON, a very large percentage of data and open data published on the web, remains tabular in nature. (Jeni Tennison, one of the two co-chairs of the W3C CSV on the Web working group claims that ``over 90% of the data published on data.gov.uk is tabular data''.) Tabular data is most commonly published in the form of comma separated values (CSV) files because such files are open and therefore processable by numerous tools, and tailored for all sizes of files ranging from a number of KBs to several TBs. Despite these advantages, working with CSV files is often cumbersome because they are typically not accompanied by a //schema// that describes the file's structure (i.e., ``the second column is of integer datatype'', ``columns are delimited by tabs'', etc) and captures its intended meaning. Such a description is nevertheless vital for any user trying to interpret the file and execute queries or make changes to it.
+In this master thesis project, the student will emperically validate on real-world datasets the extent to which graphs can be decomposed into graphs for which subgraph isomorphism is tractable, and run experiments to validate the effectiveness of the proposed method in terms of filtering power.
-In other data models, the presence of a schema is also important for query optimization (required for scalable query execution if the file is large), as well as other static analysis tasks. Finally, schemas are a prerequisite for unlocking huge amounts of tabular data to the Semantic Web.
-In recognition of this problem, the CSV on the Web Working Group of the World Wide Web Consortium argues for the introduction of a schema language for tabular data to ensure higher interoperability when working with datasets using the CSV or similar formats.
-The objective of this master thesis is to implement a recent proposal for such a schema language named SCULPT (http://arxiv.org/abs/1411.2351). Concretely, this entails:
-  * proposing an elegant concrete syntax for SCULPT schemas
-  * implement both the in-memory and streaming validation algorithms of SCULPT proposed in http://arxiv.org/abs/1411.2351
-  * extend the SCULPT proposal, by investigating how SCULPT can be combined with complementary features recently proposed by the W3C CSV on the Web Working group (http://www.w3.org/2013/csvw/wiki/Main_Page)
-  * and in particular, extend sculpt with features that allow tabular files to be converted into RDF
-  * create associated tooling for SCULPT (i.e., parser and serializer generator, in the spirit of data description tools)
-\\
-**Deliverables** of this master thesis project:
-  - detailed description of the SCULPT proposal (document)
-  - overview of the state of the art; in particular other proposals for schema languages for tabular data (document)
-  - concrete syntax for sculpt (design document + formal grammar)
-  - implementation of SCULPT validation algorithms (software artifact)
-  - extension of sculpt with features for converting into RDF (document + software)
-**Interested?** Contact: [[stijn.vansummeren@ulb.ac.be|Stijn Vansummeren]]
-**Status**: already taken
-===== Engineering a runtime system and compiler for AQL =====
-Automatically extracting structured information from text is a task that has been pursued for decades.Since most analytics over text involves information extraction as a first step, IE is a very important part of data analysis in the enterprise today.
-In 2005, researchers at the IBM Almaden Research Center developped a new system specifically geared for practical information extraction in the enterprise. This effort lead to SystemT, a rule-based IE system with an SQL-like declarative language named AQL (Annotation Query Language). The declarative nature of AQL enables new kinds of tools for extractor development, and draws upon known techniques form query processing in relational database management systems to offer a cost-based optimizer that ensures high-througput performance. Recent research into the foundations of AQL (http://researcher.watson.ibm.com/researcher/files/us-fagin/jacm15.pdf) has shown that, as an alternative, it is also possible to build a runtime system for AQL based on special kinds of finite state automata. A potential benefit of this alternate runtime system is that text files need only be processed once (instead of multiple times in the cost-based optimizer backend) and may hence provide greater throughput. On the other hand, the alternate system can sometimes have larger memory requirements than the cost-based optimizer backend.
-The objective of this master thesis is to design and engineer a runtime system and compiler for (a fragment) of AQL based on finite state automata. Ideally, to obtain the best performance, these automata should be compiled into machine-code when executed. For this compilation, the following technologies should be used:
-  * A a high-level language to construct the compiler (Scala, http://scala-lang.org/)
-  * Use of Lightweight Modular Staging (LMS for short) for generating low-level portable assembly from the automata at runtime (http://scala-lms.github.io/)
-  * Use of LLVM (http://llvm.org/) as a portable assembly code and corresponding translator to machine code.
-Getting aquaintend with these technologies is part of the master thesis objective.
-**Validation of the approach** The thesis should propose a benchmark collection of AQL queries and associated input text files that can be used to test the obtained automaton-based AQL compiler and compare its performance against the reference, cost-based optimizer of SystemT.
-**Deliverables** of the master thesis project:
-  - An overview of AQL, SystemT, and its cost-based optimizer and evaluation engine. (document)
-  - A description of how AQL can be evaluated by means of so-called vset finite state automata. (document)
-  - A detailed desription of the state of the art in evaluating finite state automata. (document)
-  - Identification of the AQL syntaxt that is to be supported. (specification)
-  - The AQL compiler (software artifact)
-  - A benchmark set of AQL queries and associated data sets for the experimental validation
-  - An experimental validation of the compiler, comparing efficiency of compiled queries against the cost-based reference compiler.
-\\
-**References about SystemT**:
-  * [[http://almaden.ibm.com/cs/projects/avatar/icde2008.pdf|An Algebraic Approach to Rule-Based Information Extraction]]
-  * [[http://www.sigmod.org/publications/sigmod-record/0812/p007.special.krishnamurthy.pdf|SystemT: A System for Declarative Information Extraction]]
-\\
-**References about finite state automata evaluation**:
-  * Regular expression pattern matching can be simple and fast. http://swtch.com/~rsc/regexp/regexp1.html
-  * Regular Expression Matching: the Virtual Machine Approach http://swtch.com/~rsc/regexp/regexp2.html
-  * Regular Expression Matching in the Wild http://swtch.com/~rsc/regexp/regexp3.html
-  * [[http://www.diku.dk/kmc/documents/AiPL-CrashCourse.pdf|A Crash-Course in Regular Expression Parsing and Regular Expressions as Types.]]
-\\
 **Interested?** Contact : [[stijn.vansummeren@ulb.ac.be|Stijn Vansummeren]]
-\\
 **Status**: taken
-===== Structural compression of relational databases =====
+=====Extending SPARQL for Spatio-temporal Data Support=====
-Recent research in database management systems at ULB has shown how to theoretically construct succinct (compressed) representations for relational databases and semantic web databases. The advantage of these succinct representations is that they allow querying directly **on the succinct representation**, without needing to consult the underlying database.
+[[http://www.w3.org/TR/rdf-sparql-query/|SPARQL]] is the W3C standard language to query RDF data over the semantic web. Although syntactically similar to SQL,  SPARQL is based on graph matching. In addition, SPARQL is aimed, basically, to query alphanumerical data.
+Therefore, a proposal to extend SPARQL to support spatial data, called  [[http://www.opengeospatial.org/projects/groups/geosparqlswg/|GeoSPARQL]], has been presented to the Open Geospatial Consortium.
+In this thesis we propose to (1) perform an analysis of the current proposal for GeoSPARQL; (2) a study of  current implementations of SPARQL that support spatial data; (3) implement simple extensions for SPARQL to support spatial data, and use these language in real-world use cases.
-The goal of this thesis is to study scalable algorithms for constructing the actual succinct representations. Some in-memory algorithms are already known, but given the large size of typical database, distributed and out-of-core alternatives need to be found.
+   * Contact: [[ezimanyi@ulb.ac.be|Esteban Zimányi]]
-**Deliverables**:
-  * Overview of the state of the art in main-memory, and distributed (bi)simulation-based compression algorithms (document)
-  * Description of the simulation-based compression algorithm to implement (document)
-  * Selection of the distribution framework (Actors, Pregel, ...) (document)
-  * Simulation algorithm (software artifact)
-  * Experimental analysis of distributed algorithm on a number of datasets. (document)
-**Interested?** Contact : [[stijn.vansummeren@ulb.ac.be|Stijn Vansummeren]]
+====== MFE 2019-2020 : Spatiotemporal Databases ======
+Moving object databases (MOD) are database systems that can store and manage moving object data. A moving object is a value that changes over time. It can be spatial (e.g., a car driving on the road network), or non-spatial (e.g., the temperature in Brussels). Using a variety of sensors, the changing values of moving objects can be recorded in digital formats. A MOD, then, helps storing and querying such data. A couple of prototypes have also been proposed, some of which are still active in terms of new releases. Yet, a mainstream system is by far still missing. Existing prototypes are merely research. By mainstream we mean that the development builds on widely accepted tools, that are actively being maintained and developed. A mainstream system would exploit the functionality of these tools, and would maximize the reuse of their ecosystems. As a result, it becomes more closer to end users, and easily adopted in the industry.
-**Status**: available
+In our group, we are building MobilityDB, a mainstream MOD. It builds on PostGIS, which is a spatial database extension of PostgreSQL. MobilityDB extends the type system of PostgreSQL and PostGIS with ADTs for representing moving object data. It defines, for instance, the tfloat for representing a time dependant float, and the tgeompoint for representing a time dependant geometry point. MobilityDB types are well integrated into the platform, to achieve maximal reusability, hence a mainstream development. For instance, the tfloat builds on the PostgreSQL double precision type, and the tgeompoint build on the PostGIS geometry(point) type. Similarly MobilityDB builds on existing operations, indexing, and optimization framework.
-===== A Scala-based runtime and compiler for Distributed Datalog =====
+This is all made accessible via the SQL query interface. Currently MobilityDB is quite rich in terms of types and functions. It can answer sophisticated queries in SQL. The first beta version has been released as open source April 2019 (https://github.com/ULB-CoDE-WIT/MobilityDB).
-Datalog is a fundamental query language in datamanagement based on logic programming. It essentially extends select-from-where SQL queries with recursion. There is a recent trend in data management research to use datalog to specify distributed applications, most notably on the web, as well as do inference on the semantic web. The goal of this thesis is to engineer a basic **distributed datalog system**, i.e., a system that is capable of compiling & running distributed datalog queries. The system should be implemented in the Scala programming language. Learning Scala is part of the master thesis project.
+The following thesis ideas contribute to different parts of MobilityDB. They all constitute innovative development, mixing both research and development. They hence will help developing the student skills in:
+  * Understanding the theory and the implementation of moving object databases.
+  * Understanding the architecture of extensible databases, in this case PostgreSQL.
+  * Writing open source software.
-The system should incorporate recently proposed worst-case join algorithms (i.e., the [[http://arxiv.org/abs/1210.0481|leapfrog trie join]]) and employ known local datalog optimizations (such as magic sets and QSQ.)
-**Validation of the approach** The thesis should propose a benchmark collection of datalog queries and associated data workloads that be used to test the obtained system, and measure key performance characteristics (elasticity of the system; memory frootprint; overall running time, ...)
+=====JDBC driver for Trajectories=====
+An important, and still missing, piece of MobilityDB is Java JDBC driver, that will allow Java programs to establish connections with MobilityDB, and store and retrieve data. This thesis is about developing such a driver. As all other components of PostgreSQL, its JDBC driver is also extensible. This documentation gives a good explanation of the driver and the way it can be extended:
+https://jdbc.postgresql.org/documentation/head/index.html
+It is also helpful to look at the driver extension for PostGIS:
+https://github.com/postgis/postgis-java
+As MobilityDB build on top of PostGIS, the Java driver will need to do the same, and build on top of the PostGIS driver. Mainly the driver will need to provide Java classes to represent all the types of MobilityDB, and access the basic properties.
-**Deliverables**:
+**Interested?**
-  * Semantics of datalog; overview of known optimization strategies (document)
+  * Contact : [[ezimanyi@ulb.ac.be|Esteban Zimanyi]]
-  * Description of the leapfrog trie join (document)
-  * Datalog system (software artifact)
-  * Experimental analysis of developped system on a number of use cases (document)
-\\
-**Interested?** Contact : [[stijn.vansummeren@ulb.ac.be|Stijn Vansummeren]]
 **Status**: available
-===== Design and Implementation of a Curriculum Revision Tool =====
+=====Mobility data exchange standards=====
+Data exchange standards allow different software systems to integrate together. Such standards are essential in the domain of mobility. Consider for example the case of public transportation. Different vehicles (tram, metro, bus) come from different vendors, and are hence equipped with different location tracking sensors. The tracking software behind these vehicle use different data formats. These software systems need to push real time information to different apps. To support the passengers, for example, there must be a mobile or a Web app to check the vehicle schedules and to calculate routes. This information shall also be open to other transport service providers and to routing apps. This is how google maps, for instance, is able to provide end to end route plans that span different means of transport.
-Stijn Vansummeren (WIT), Frédéric Robert (BEAMS)
+The goal of this thesis is to survey the available mobility data exchange standards, and to implement in MobilityDB import/export functions for the relevant ones. Examples for these standards are:
+  * GTFS static, https://developers.google.com/transit/gtfs/
+  * GTFS realtime, https://developers.google.com/transit/gtfs-realtime/
+  * NeTEx static, http://netex-cen.eu/
+  * SIRI, http://www.transmodel-cen.eu/standards/siri/
+  * More standards can be found on http://www.transmodel-cen.eu/category/standards/
-This master thesis project concerns the analysis, design, and implementation of a software system that can assist in the revision of teaching curricula (also known as teaching programs).
-The primary targetted functionalities of the software system are as follows:
-  * It should allow to make different versions of the teaching programs, much in the same way as version control systems like GIT and subversion offer the possibility to make different "development branches" of a program's source code.
+**Interested?**
-  * It should allow an extensible means to check the modified program for inconsistentcies. (For example, if course X has course Y as prerequisite, then course Y should not be scheduled in 2nd semester and X in 1st semester. Moreover, the total number of ECTS of all courses should be at most 60 ECTS. )
+  * Contact : [[ezimanyi@ulb.ac.be|Esteban Zimanyi]]
-  * It should allow to analyze the modifications proposed in the teaching programs, and summarize the impact that these changes could have on other programs. (For example, if a course is removed from the computer science curriculum, it should be flagged that it should also be removed from all curricula that included the course.)
-  * It should load data from (and preferably, save data to) the ULB central administration database.
-  * It should give suggestions concerning the impact of the modifications on the course schedules.
-A proof-of-concept implementation of a revision tool that supports the first two requirements above is currently being developped in the context of a PROJH402 project. The MFE student that selects this topic is expected to:
+**Status**: available
-  * Develop this prototype to a production-ready implementation.
-  * Implement the communication with the central ULB database.
-  * Implement the impact analysis concerning the course schedules.
-  * Interact with the administration of the Ecole Polytechnique to fine-tune the above requirements; test the implementation; and integrate remarks after testing
-\\
+=====Visualizing spatiotemporal data=====
-**Interested?** Contact : Stijn Vansummeren (stijn.vansummeren@ulb.ac.be), Frédéric Robert <frrobert@ulb.ac.be>
+Data visualization is essential for understanding and presenting it. starting with the temporal point, which is the database representation of a moving point object. Typically, it is visualized in a movie style, as a point that moves over a background map. The numerical attributes of this temporal point, such as the speed, are temporal floats. These can be visualized as function curves from the time t to the value v.
+The goal of this thesis is to develop a visualization tool for the MobilityDB temporal types. The architecture of this tool should be innovative, so that it will be easy to extend it with more temporal types in the future. should be This tool should be integrated as an extension of a mainstream visualization software. A good candidate is QGIS (https://www.qgis.org/en/site/). The choice is however left open as part of the survey.
-**Status?** Already taken
+**Interested?**
+  * Contact : [[ezimanyi@ulb.ac.be|Esteban Zimanyi]]
-===== Semi-Supervised Entity Resolution =====
+**Status**: available
-Toon Calders (WIT)
-In the big data era large collections of data have become available for analysis. These data, however, often come from different data sources and may contain errors. Consider for instance a company that wants to combine data from marketing and sales in order to see to what extent the targeted marketing campaign has been successful in attracting new customers. A key operation in this analysis is the identification of which records from marketing and sales refer to the same person. In this way it can be determined which targeted potential customers were already clients, and of the contacted non-clients, which ones reacted to the marketing campaign. Furthermore, most likely the records of marketing are far less reliable and formatted differently than those of sales. For instance, the marketing records won't usually contain a client number. The process of linking these sources together and identifying which records refer to the same person is know as entity resolution. Most existing approaches for entity resolution use either a fixed set of pre-determined rules, which may be sub-optimal for the problem at hand, or are based on learning classifiers which requires large amounts of labelled data.
+=====Data modeling of spatiotemporal regions=====
+In moving object databases, a lot of attention has been given to moving point objects. Many data model have been proposed for this. Less attention has been given to moving region objects. Imagine a herd of animals that moves together in the wild. At any time instant, this herd can be represented using a spatial region, e.g., their convex hull. Over time, this regions changes place and extent. A spatiotemporal region is an abstract data type that can represent this temporal evolution of the region.
-In this thesis you will study the possibility of entity-resolution in the absence of large collections of labelled data, by exploiting redundancies in the features with which records can be compared in combination with an active learning approach in which volunteers can be asked to label some examples on the fly.
+This thesis is about proposing a data model for spatiotemporal regions, and implementing it in MobilityDB. This includes surveying the literature on moving object databases, and specifically on spatiotemporal reigons, proposing a discrete data model, implementing it, and implementing the basic data base functions and operations to make use of it.
-\\
-**Interested?** Contact [[toon.calders@ulb.ac.be|Toon Calders]]
-===== Using Non-Redundant Sequential Pattern Mining for Process Discovery =====
+**Interested?**
-Toon Calders (WIT)
+  * Contact : [[ezimanyi@ulb.ac.be|Esteban Zimanyi]]
-Process mining is the act of deriving a process model, such as for instance a Petri-net or a BPMN model, based on an event log. An example of such a log could be all events that an insurance company undertakes for pricing a car insurance based on a request from a client. Events could be looking up if the client has been blacklisted, his or her history w.r.t. car accidents, estimating the risk based on car type, age and gender of the requester, making a proposal, soliciting the agreement of the client, in case of disagreement, contacting a manager to approve a special offer, etc. Based on several traces for different clients may allow the automatic reconstruction of a process model. There exist several approaches for process mining, including footprint based algorithms such as Alpha, Alpha+, heuristic algorithms including heuristics miner, genetic algorithms, region based methods, etc. The goal of this thesis is to explore the possibility of using current state-of-the-art data mining algorithms for sequence and episode mining as a basis of a new and improved version of the alpha-algorithm.
+**Status**: available
-Van der Aalst, W. M. (2011). Process Mining: Discovery, Conformance and Enhancement of Business Processes. Springer.
-Interested? Contact [[toon.calders@ulb.ac.be|Toon Calders]]
-===== Mining patterns for compression =====
-Toon Calders (WIT)
-Data mining is the research discipline that studies the extraction of information from large amounts of data. One of the typical data mining tasks is pattern mining where we try to find regularities that occur frequently in a dataset. The prototypical example is that of a supermarket storing for every customer visiting the supermarket, the transaction; that is, the set of items that were bought by that customer. The frequent itemset mining problem now is to detect which combinations of products were more often sold together than a given threshold. One of the major problems of pattern mining algorithms, however, is the enormous amount of redundant patterns they generate; for instance, very popular items, such as toilet paper, tend to appear in many frequent combinations purely due to chance. In order to deal with this problem, techniques based upon compression and minimum description length were proposed to reduce the number of patterns. The rationale behind the minimal description length principle is that a set of patterns that describes well what is happening in the dataset should allow for a good compression. For a collection of patterns, the quality is measured as the description length of the patterns plus the size of the data compressed with these patterns. For instance, if the pattern {bread, milk, butter} has a high frequency, we could opt to replace every occurrence of this pattern by a special code, effectively reducing the encoding length of the data. Surprisingly, however, the MDL principle was until now only used to rule out redundant patterns, and it has not been researched yet how well the discovered patterns actually do compress the data as compared to compression algorithms such as Lempel–Ziv–Welch.
-Hence, in this highly research oriented graduation project, two research questions are central: (1) How good do non-redundant pattern sets based on MDL allow compressing data, and (2) Can we extract useful patterns from existing compression algorithms?
-Interested? Contact [[toon.calders@ulb.ac.be|Toon Calders]]
-=====Publishing and Using Spatio-temporal Data on the Semantic Web=====
-[[http://www.w3c.org/|RDF]] is the [[http://www.w3c.org/|W3C]] proposed framework for representing information
-in the Web. Basically, information in RDF is represented as a set of triples of the form (subject,predicate,object).  RDF syntax is based on directed labeled graphs, where URIs are used as node labels and edge labels. The [[http://linkeddata.org/|Linked Open Data]] (LOD) initiative is aimed at extending the Web  by means of publishing various open datasets as RDF,  setting RDF links between data items from different data sources.  Many companies  and government agencies are moving towards publishing data following the LOD initiative.
-In order to do this, the original data must be transformed into Linked Open Data. Although most of these data are alphanumerical, most of the time they contained  a spatial or spatio-temporal component, that must also be transformed. This can be exploited
-by application providers, that can build attractive and useful applications, in particular, for devices like mobile phones, tablets, etc.
-The goals of this thesis are: (1) study the existing proposals for mapping spatio-temporal data into LOD; (2) apply this mapping to a real-world case study (as was the case for the [[http://www.oscb.be/|Open Semantic Cloud for Brussels]] project; (3) Based on the produced mapping, and using existing applications like the [[http://linkedgeodata.org/|Linked Geo Data project]], build applications that make use of LOD for example, to find out which cultural events are taking place at a given time at a given location.
-    * Contact: [[ezimanyi@ulb.ac.be|Esteban Zimányi]]
-=====Extending SPARQL for Spatio-temporal Data Support=====
-[[http://www.w3.org/TR/rdf-sparql-query/|SPARQL]] is the W3C standard language to query RDF data over the semantic web. Although syntactically similar to SQL,  SPARQL is based on graph matching. In addition, SPARQL is aimed, basically, to query alphanumerical data.
-Therefore, a proposal to extend SPARQL to support spatial data, called  [[http://www.opengeospatial.org/projects/groups/geosparqlswg/|GeoSPARQL]], has been presented to the Open Geospatial Consortium.
-In this thesis we propose to (1) perform an analysis of the current proposal for GeoSPARQL; (2) a study of  current implementations of SPARQL that support spatial data; (3) implement simple extensions for SPARQL to support spatial data, and use these language in real-world use cases.
-   * Contact: [[ezimanyi@ulb.ac.be|Esteban Zimányi]]