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teaching:projh402 [2020/10/03 18:14] ezimanyi [VODKA Indexes for MobilityDB] |
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| Mobility databases (MOD) are database systems that can store and manage moving object geospatial trajectory data. A moving object is an object that changes its location over time (e.g., a car driving on the road network). Using a variety of sensors, the location tracks of moving objects can be recorded in digital formats. A MOD, then, helps storing and querying such data. A couple of prototype systems have been proposed by research groups. Yet, a mainstream system is by far still missing. 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. | Mobility databases (MOD) are database systems that can store and manage moving object geospatial trajectory data. A moving object is an object that changes its location over time (e.g., a car driving on the road network). Using a variety of sensors, the location tracks of moving objects can be recorded in digital formats. A MOD, then, helps storing and querying such data. A couple of prototype systems have been proposed by research groups. Yet, a mainstream system is by far still missing. 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. | ||
| - | Towards filling this gap, our group is building the [[https://github.com/MobilityDB/MobilityDB|MobilityDB]] system. It builds on [[https://postgis.net/|PostGIS]], which is a spatial database extension of [[https://www.postgresql.org/|PostgreSQL]]. MobilityDB extends the type system of PostgreSQL and PostGIS with ADTs for representing moving object data. It defines, for instance, the tgeompoint type 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 tgeompoint type builds on the PostGIS geometry(point) type. Similarly MobilityDB builds on existing operations, indexing, and optimization framework. | + | Towards filling this gap, our group is building the [[https://github.com/MobilityDB/MobilityDB|MobilityDB]] system. It builds on [[https://postgis.net/|PostGIS]], which is a spatial database extension of [[https://www.postgresql.org/|PostgreSQL]]. MobilityDB extends the type system of PostgreSQL and PostGIS with abstract data types (ADTs) for representing moving object data. It defines, for instance, the tgeompoint type 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 tgeompoint type builds on the PostGIS geometry(point) type. Similarly MobilityDB builds on existing operations, indexing, and optimization framework. |
| MobilityDB supports SQL as query interface. Currently it is quite rich in terms of types and functions. It is incubated as community project in [[https://www.osgeo.org/projects/mobilitydb/|OSGeo]], which certifies high technical quality. | MobilityDB supports SQL as query interface. Currently it is quite rich in terms of types and functions. It is incubated as community project in [[https://www.osgeo.org/projects/mobilitydb/|OSGeo]], which certifies high technical quality. | ||
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| MobilityDB provides [[https://habr.com/en/company/postgrespro/blog/444742/|GiST]] and [[https://habr.com/ru/company/postgrespro/blog/446624/|SP-GiST]] indexes for temporal types. These indexes are based on bounding boxes, that is, the nodes of the index tree store a bounding box that keeps the mininum and maximum values of each of the dimensions where X, Y, Z (if available) are for the spatial dimension and T for the temporal dimension. The reason for this is that a temporal type (for example, a moving point representing the movement of a vehicle) can have thousands of timestamped points and keeping all these points for each vehicle indexed in a table is very inefficient. By keeping the bounding box only it is possible to quickly filter the rows in a table and then a more detailed analysis can be made for those rows selected by the index. | MobilityDB provides [[https://habr.com/en/company/postgrespro/blog/444742/|GiST]] and [[https://habr.com/ru/company/postgrespro/blog/446624/|SP-GiST]] indexes for temporal types. These indexes are based on bounding boxes, that is, the nodes of the index tree store a bounding box that keeps the mininum and maximum values of each of the dimensions where X, Y, Z (if available) are for the spatial dimension and T for the temporal dimension. The reason for this is that a temporal type (for example, a moving point representing the movement of a vehicle) can have thousands of timestamped points and keeping all these points for each vehicle indexed in a table is very inefficient. By keeping the bounding box only it is possible to quickly filter the rows in a table and then a more detailed analysis can be made for those rows selected by the index. | ||
| - | However, the drawback of keeping a single bounding box for the whole trajectory makes that the index is not very selective as shown in the following figure (extracted from a presentation by Oleg Bartunov from ProstgresPro) | + | However, the drawback of keeping a single bounding box for the whole trajectory makes that the index is not very selective as shown in the following figure (extracted from a presentation by Oleg Bartunov from PostgresPro) |
| {{:teaching:gist.png?400|}} | {{:teaching:gist.png?400|}} | ||
| - | The goal of the project is to define [[https://www.pgcon.org/2014/schedule/events/696.en.html|VODKA indexes]] that enable us to store in the index multiple bounding boxes associated to each row in the table as shown in the following figure | + | The goal of the project is to define [[https://www.pgcon.org/2014/schedule/events/696.en.html|VODKA indexes]] for MobilityDB, which enable us to store in the index multiple bounding boxes (one per segment) associated to each row in the table as shown in the following figure |
| {{:teaching:vodka.png?400|}} | {{:teaching:vodka.png?400|}} | ||