# QB4 MobOLAP: A Vocabulary Extension for Mobility OLAP on the Semantic Web
## 2 Related Works
### Geospatial Semantic Web  
The Spatiotemporal Multidimensional Data model on the SW starts from the Spatial SW, commonly referred to as Geospatial SW. The development of Geospatial SW began with finding a new retrieval method for geospatial data built on the semantics of spatial and ontologies developed at the University of Maine [40]. Then, the W3C SW Interest Group standardized Basic Geo Vocabulary using WGS84 as a reference datum [41]. [PERSON] et al. stated that the web has a significant amount of spatial and temporal data, and the technology of SW could potentially make the accessibility and usefulness of data better. Because of SPARQL's inability to query complex spatial and temporal data, [PERSON] et al. proposed a new query language, SPARQL-ST, an extension of SPARQL for complex spatiotemporal queries. This research suggested a formal syntax and semantics and added spatial variables and constructs to manipulate temporal triples in SPARQL-ST, and was applied as a prototype built on top of a commercial DBMS [42]. Their work has many features but is still limited to essential operation for spatiotemporal operations, and is not applied for aggregation and analytical query functions. Research on spatiotemporal data on the SW has been successfully implemented, such as Linked Geospatial Data in the UK government, followed by the manufacture of geospatial datasets by the Ordnance Survey Company for regions in the UK. These implementations could be accessed using SPARQL Endpoints [6]. Linked data are becoming popular with the advent of Geonames, a dataset in the form of linked data that collects spatial and thematic information for place names in different hemispheres and in various languages. The information stored in it is in the form of latitude, longitude, altitude, and population, and the administrative information is consistent with the 1984 World Geodetic System (WGS84) rules. Furthermore, there is LinkedGeodata, a linked data that is an SW infrastructure converted from OpenStreetMap. This linked data helps integrate and aggregate data related to maps [43] and can be easily queried with SPARQL. This approach attracts many researchers as a promising spatial linked data paradigm, but this approach still does not cover temporal data. The temporal aspect then entered as a Spatiotemporal SW in the development of YAGO2 ontology, a continuation of YAGO knowledge-based ontology, where entities, events, and facts are combined with space-time information. YAGO2 was developed by automating Wikipedia, GeoNames, and WordNet. At present, YAGO2 contains 447 million facts and 9.8 million entities. YAGO2 uses the SPOTL model data (five tuples), an ex tension of SPO (3 tuples). Entities on YAGO2 are assigned a period, while the fact is assigned a time point or period [44]. YAGO2 became an excellent way to enrich large spatiotemporal knowledge-based data, but it did not have query functions for its spatiotemporal representation. Furthermore, a query language, with the addition of geographic features to SPARQL, was developed, namely GeoSPARQL. GeoSPARQL is an SW vocabulary that provides geospatial data representation [45]. GeoSPARQL has two essential parts: an ontology for the storing of geospatial objects and query functions for the processing of relationships between the geospatial entities. The ontology was developed from the OGC standards, which have expressive concepts and terminology. The ontology of the GeoSPARQL is built to be small so that it can be easily understood and attached. The GeoSPARQL ontology has two main classes: Feature and Geometry. A Feature is an entity with spatial attributes. An example of the Feature is a building, statue, palace, lake, etc. Geometry is a shape, for example, a point, line, triangle, hexagon, etc., representing a feature's spatial location. The third class, SpatialObject, is a superclass of both Feature and Geometry. GeoSPARQL became a geospatial RDF standard from W3C for data modeling and querying [46].