# Smart Environmental Data Infrastructures: Bridging the Gap between Earth Sciences and Citizens
## 5 Data Searching and Browsing
### Geospatial Data Searching and Browsing  
Geospatial data searching and browsing over vector features are generally supported by the spatial query capabilities of spatial databases [6; 7]. Spatial extensions of relational and object-relational DBMSs are based on OGC [26] and ISO [98] standards. Efficiency is achieved through spatial indexing structures and spatial query processing techniques. Declarative querying over raster coverages is not supported in standard SQL. In spite of this, some spatial database implementations such as the PostGIS ([[https://postgis.net/](https://postgis.net/)]([https://postgis.net/](https://postgis.net/))) extension of PostgreSQL incorporate already a raster data type. However, on the one hand, raster queries are complex in the sense that raster arrays are nested in tuples and the user must combine raster functions with SQL, and on the other hand the efficiency of the implementation is still not appropriate. Specific managers for array datasets are also available [29; 30] that incorporate efficient declarative query capabilities. In spite of all the above solutions, effective and efficient integrated querying of raster and vector datasets has still not been achieved by any solid implementation [54]. The implementation of geospatial data discovering and access infrastructures on the web are now supported by OGC standard service interfaces and INSPIRE recommendations [99; 100]. As it is illustrated in the UML components diagram of Figure 10, geospatial searching, and browsing client applications may discover the existence of geospatial datasets using a Catalog Server that implements the OGC catalog service (CSW) standard interface [15]. This service enables filtering (including spatial and temporal conditions) over sets of geospatial metadata, usually modeled according to ISO 19115. These metadata may be harvested from Geospatial Data Servers, which provide access to datasets of vector features and raster coverages. Structured data searching over vector features and raster coverages are provided through OGC Web Feature Service (WFS) [16] and Web Coverage Service (WCS) [17] standard interfaces, respectively. Browsing geospatial datasets has to be done through map based interfaces. Map rendering may be done at the client side using the data retrieved through WFS and WCS, however, server-side map rendering is also generally supported by Geospatial Data Server implementations through OGC Web Map Service (WMS) [18] standard interface. Client-side rendering of maps enables more flexible and interactive interfaces, but on the other hand server-side map generation enables the browsing of very large datasets with light-weight clients, as those usually available in mobile devices. If we focus now on environmental observation and model data, various infrastructures and platforms have already been constructed. A first example is the Global Earth Observation System of Systems (GEOSS) Common Infrastructure [83; 101], which provides services to discover, search and access Earth Observation data sources. A key element of this infrastructure is its Discovery and Access Broker (DAB) framework, which includes brokering solutions for data discovery, data access, and semantic interoperability. The taxonomy proposed in [90] classifies web services to ease their  
Figure 10: Illustration of geospatial data discovering, search and browsing in OGC Spatial Data Infrastructures. incorporation in the GEOSS Component and Service Registry. The main types of services according to this taxonomy are: (i) Data Access Services, (ii) Catalog/Registry Services, (iii) Portrayal and Display Services and (iv) Data Transformation Services. Notice that except Data Transformation Services, which deal with data processing, the other three types of services are needed for data discovering, access and browsing.