Lab News


2019-08-19: Walid served as Panelist in SSTD 2019 in Vienna, Austria. The topic of the panel was about reflecting on the past 30 years of the SSTD Symposium. Surprisingly, I also attended the first symposium in 1989 in Santa Barbara. At that time, the name of the symposium was SSD (the T for temporal was not there yet). 

2019-06-11: Walid delivered a keynote speech at the 2019 IEEE Mobile Data Management conference in Hong Kong. The title of the keynote was: The Dos and Don’ts of Location+X Data Management: A “Systems Perspective”.

2019-Spring-Graduations: Congratulations to Amr Ebaid who graduated this Spring and has joined Google. I wish you all the best!

2019-04-11: We received the best demo award in the IEEE ICDE 2019 for the Explainability demo. Congratulations to Amr Ebaid… Good Ending!

2018-Fall-Graduations: Congratulations to Amgad Madkour who graduated in the fall and have joined Microsoft AI&R. I will miss you Amgad, and I wish you all the best!

2018-10-13: New students

-       The following graduate students joined my research group: Abdullah Al Mamun (Ph.D.) and Varshika Srinivasavaradhan (Masters with thesis). Also, Ph.D. Student Serkan Uzunbaz rejoined my research group after some disappearance in Industry. 

-       The following undergraduate students have been doing research with me during spring, summer, and fall of this year (2018): Daksh Jotwani (Fall), Aaron Jon Neustedter (Fall), Piyush Jeneja (Fall), Xu (Amber) He (Spring and Summer), Harsh Patel (Summer), Nameer Qureshi (Spring and Summer),  Jaideep Juneja (Spring).


2019-01-07: Walid is co-chairing the PC for the 16th International Symposium on Spatial and Temporal Databases along with Christian Jensen and Kjetil Nørvåg. SSTD is held every two years. This year, it will held in Vienna, Austria in August.

2018-09-01: Along with Ahmed Mahmood and Sri Punni (Former Masters students, now at Amazon), we finished Part 3 of the survey on spatio-temporal access methods. Part 1 covered the spatio-temporal access methods up to 2003 and was published in the IEEE Data Engineering Bulletin in 2003. Part 2 covered the spatio-temporal access methods from 2003 to 2010 and was published in the IEEE Data Engineering Bulletin in 2010. Part 3 covers the spatio-temporal access methods from 2010 to 2017 and will be published in the Springer GeoInformatica Journal in 2018. Part 3 is extensive, and also covers a new class of spatio-temporal and textual access methods.


2018-08-01: Walid was appointed as the new Editor-in-Chief of the ACM Transactions on Spatial Algorithms and Systems.


2018-Summer Graduations: During this summer, four Ph.D. students graduated. In the order of their graduation, Ahmed R. Mahmood (now at Google), Elkindi Rezig (will move to MIT as Postdoc with Professor Mike Stonebraker), Mohamed A. Hassan (now at Oracle), Yongyang Yu (now at Facebook). Congratulations to all! I will miss our good discussions.


2018-Summer Internship News: This summer, Amgad Madkour went to Microsoft to work in the AI+R group. The rest of the students remained at Purdue to finalize their Ph.D. dissertations to graduate. 


2018-Spring and Summer New Publications: This spring, we published several good papers. 

-       Congratulations to Mohamed Hassan for publishing his GRFusion paper at EDBT 2018, and a demo of the same system in SIGMOD 2018. Mohamed’s graph sketching paper was also published in SSDBM 2018. Good ending Mohamed! 

-       Congratulations to Amgad Madkour for publishing his RDF query processing series of papers that reflects his RDF systems work. He published two papers in the Semantic Big Data Workshop associated with SIGMOD 2018, and published his WORQ paper in ISWC2018. Keep up the good work, Amgad!

-       Congratulations to Ahmed Mahmood and Tatiana Kuznetsova for the publication of their limited-trajectories indexing paper into the ACM TSAS. This is our first paper in this relatively new journal.


2017-05-14: Walid Gave a keynote talk titled: Location + X Big Data Systems: Challenges and Some Solutions at the Fourth International ACM SIGMOD Workshop on Managing and Mining Enriched Geo-Spatial Data (GeoRich 2017) Co-located with SIGMOD/PODS 2017 in Chicago, IL, USA.


2017: Summer Internship News: Saber and Samy are heading to MSR in two different groups. Tatiana is heading to Teradata. Best wishes to all for a successful summer!


2016-07-19: VLDB 10-Year Best-Paper Award

Walid, Prof. Mohamed Mokbel at the University of Minnesota, and Prof. Chi-Yin Chow (Ted) at City University of Hong Kong won the VLDB 10-year best paper award for their 2006 VLDB paper titled: “The New Casper: Query Processing for Location Services Without Compromising Privacy”.  According to the VLDB (Very Large Data Bases) endowment web site (, this award is established for the author(s), whose paper appeared in the VLDB conference 10 years ago, that has the most impact on database research since then. 


This paper has a long story behind it that dates back to 1999 when the NSF started its ITR program (ITR is short for Information Technology Research). The target of this program was to solicit groundbreaking and innovative research in contrast to incremental or delta research. At the time, Walid had the vision that location data and location services should be ubiquitous. Satellites were already established and out there but at the same time GPS devices were unnecessarily expensive and not widely spread. So, why not make location detection devices, especially GPSs, ubiquitous? What if all objects in space know their locations? What services can be offered? How computing will be affected? How databases and query processing engines and indexing techniques will scale to accommodate floods of location data?  Of course, smart devices with GPSs were not there yet as of 1999. Probably, this is what made this project qualify as an NSF-ITR groundbreaking project at the time. Professors Susanne Hambrusch, Sunil Prabhakar, and Walid teamed up to write a proposal to the NSF ITR program to seek funding for the PLACE project (PLACE is short for Pervasive Location-Aware Computing Environment) that addresses database engine and query processing challenges when location data collection becomes ubiquitous. In PLACE, the assumption is that all objects in space, whether mobile or stationary, have location detection mechanisms so that each object is aware of its location. But now comes the critical part that motived the Casper paper. Not only that each object in PLACE will know its location, but also the object will report its location to the PLACE server. Now, the PLACE server will know the location of literally everyone, and at all times. The PLACE server will be receiving “streams” of location data in the form of (object identifier, location coordinates, time) as well as “streams” of user queries that request answers progressively. Examples of these progressive or “continuous” queries are: “Continuously alert me when someone steps into my backyard”, “Alert me when one of my pets is away by more than 100 feet from my house”, “as I am driving on the highway, continuously report the three-nearest gas stations or hotels”, etc. Other location services were envisioned given PLACE including  (1) Assisting the visually-challenged in crossing the road (since PLACE knows the location of all objects in space around this person, it can allow the person navigate the space safely, stop a taxi cab without seeing it, etc.), (2) As one takes a photo, the camera would label all the objects at the scene by issuing a cone-shaped query to the PLACE server to get all the objects’ names in the scene, among other services. These services are offered nowadays, but back in 1999, it was a bit of a stretch (Lesson to be learned about patenting J).


Many good papers, demo systems and prototypes, as well as nice well-cited research, and several Ph.D. theses, have resulted from the PLACE project. However, many new research challenges emerged as well. The most important challenge is that of privacy. Many people feel uncomfortable sending their location information to a global server as is the case with the PLACE server. Also, when someone issues a location-based query, this person’s location is revealed. For example, the query “Find the three closest restaurants to me”, reveals the person’s current location. So, the question is: How can we process users’ queries and provide them with a wide spectrum of location services without compromising the users’ privacy? Mohamed, Ted, and Walid were the first to address this question of location privacy from a database perspective. This was the subject of their Casper paper that was published at the 2006 VLDB Conference in Seoul, Korea (the “New Casper” paper). A prototype of Casper was later demonstrated at the 2007 IEEE ICDE Conference, and finally an upgraded version and extension of the Casper algorithms were later published in the ACM TODS Journal in 2009 (the Casper* paper). The name “Casper” was inspired by the famous 1960’s cartoon character Casper, the friendly ghost. Being a ghost, Casper can hide its location while still hiding its location. The New Casper location-based server acts the same. It does not reveal users’ locations yet provides them with location services without compromising the users’ privacy.  The VLDB 2006 New Casper paper has had a broad impact once published and has been widely cited since then. 


Fast-forwarding to 2016, the vision of the PLACE project is now a reality. Almost all smart-phone devices are enabled with location-detection devices and they report the users’ current locations to location servers in a similar way to that of PLACE, e.g., taxi services, traffic and navigation services, flight status services, monitoring rare species and flocks, and gaming services. The need for nowadays location servers to follow Casper-like approaches in offering location services without compromising privacy is quite obvious now and is a necessity. 


2016 Summer: Walid will be co-chairing the PC for the IEEE MDM 2017 - 18th IEEE International Conference on 

Mobile Data Management  May 29 - June 1, 2017, KAIST, Daejeon, South Korea. 


2016: Summer Internship News: Saber and Samy are heading to MSR in two different groups, Yongyang is heading to Facebook! 


2016-4: Congratulations to Mingjie and team for the IEEE TKDE paper. Here is the paper.


2016-3: Our two demos are accepted into ICDE 2016. Congratulations to Samy and Elkindi and all team members! Here are the two demos: (Cruncher). (ORLF).


2016-2: Our accepted WSDM 2016 paper is here. Kangaroo: Workload-Aware Processing of Range Queries in Hadoop. (Kangaroo-paper).


2015-11-16: Our paper titled “Graph Indexing for Shortest-Path Finding over Dynamic Sub-Graphs” got accepted as full paper into SIGMOD 2016. Job well done Saber and Ahmed! (paper)


2015-11-5: Congratulations! Our Limo Demo paper at SIGSPATIAL 2015 got the best demo award. Here is Limo’s website:

The purpose of LIMO is to teach Computer Programming to Freshmen students using Maps and Globes as a programming toy. This prototype implementation of LIME uses Google Earth and Google Maps as the programming toy. 


2015-10-12: Congratulations! Our paper titled: “Kangaroo: Workload-Aware Processing of Range Data and Range Queries in Hadoop” has been accepted to WSDM 2016 as a full paper (18.2% acceptance rate).


2015-10-07: Some Source codes for some of the recent papers and demos:

AQWA: (VLDB 2015 Demo and VLDB 2016 full papers)

JISC: (EDBT 2014 paper)

Two-kNN work:  (VLDB 2012 paper)

kNN & Relational with the cost model (ACM SIGSPATIAL 2015 and EDBT 2015 papers)


2015-08-26: Congratulations to Ahmed Aly for successfully defending his Ph.D.  Ahmed is heading to Google!


2015-08-10: Our AQWA paper got accepted to VLDB 2016 as a full paper! Congratulations to Ahmed Aly and company! Here is the source code for AQWA on Hadoop and the AQWA paper.


2015-06: The Tornado system demo paper got accepted to VLDB 2015. Congratulations to all the Tornado team members! Here is the demo paper. The source code is to be published soon!


2015-06: The AQWA demo paper got accepted to VLDB 2015. Congratulations! Here is the demo paper and the source code for AQWA.


2015-05: Summer internships: Amgad is heading to Microsoft, Mingjie is heading to IBM Almaden Research Center, Amr is heading to Yahoo! With best wishes to all for a productive summer.


2014-12-09: Our SISAP 2014 paper got the best paper award. 


20xx: The SP-GiST software package, which is part of Walid’s NSF CAREER grant, is now part of the public distribution of PostgreSQL. Thanks to Ihab for a first experimental implementation inside Wisconsin’s Predator, to Ramy and Tabakh for an industrial strength implementation inside PostgreSQL (The ICDE2006 paper), and to the help of researchers from Moscow State University to take the PostgreSQL SPGiST codebase to the next level to make it into the public distribution of  PostgreSQL.