## 3 Proactive Geospatial Information Services (PGIS)
### Concept of PGIS
#### 3.1.1 Typical Geospatial Information Services in PGIS  
Four typical geospatial information services are defined in PGIS. They are sensor web services, data services, processing services, and social services.  
The sensor web services are built based on the SWE (Sensor Web Enablement) framework. Various sensor web applications, based on the SWE framework, have been reported in the past, including environmental monitoring [30], applications using satellite and airborne sensors [1], webcam, and vehicle-mounted sensors. For the sensor web services presented in this paper, variable sensors such as the satellite sensors, airborne sensors, traffic monitors, environmental monitors, and web cameras are connected based on SWE specifications (_i.e._, the interoperability interfaces, protocols, and metadata encodings). The sensor web services acquire data on the environment through these sensors.  
From the above sensor web services, huge amounts of data about the environment can be acquired. Ideally, users should not have to worry about heterogeneous formats, sensors and sources of data. An interoperable system of sensor data would allow users to focus on analysis tasks rather than data handling. The use of standards can help machines to communicate without human intervention. However, creating standards is challenging. The Web Ontology Language (WOL) [31] is used in this research to enable data sharing and exchange. A more challenging problem is how those data services can be linked as a whole. Linked data [26] has been presented for this task. Linked data is a platform connecting all data sets in the internet. It uses the Web to connect related data previously not linked, which has gathered awesome results by linking with other Semantic Web databases. The data services in PGIS aims at providing a well-described and linked platform for data accessing based on the above discussed technologies.  
Processing services deal with raw data on-line to support more throughout, flexible and complexity functions. The services chain technology is employed to achieve this task. The current services chain description languages follow two separate standards: the Web Service Flow Language (WSFL) of IBM and the eXtensible Markup Language (XML) LANGuage (XLANG) of Microsoft. The Business Process Execution Language (BPEL) is a new language in addition to the above two separate standards, which is based on technologies of Web Service Description Language (WSDL), XML Schema, and XML Path Language (XPath). BPEL itself defines the syntax for an XML-based programming language. The result of the complete definition of a process is a BPEL script that will be interpreted by an orchestration engine such as the Oracle BPEL Process Manager. The engine can be considered as a runtime environment that interprets the BPEL script.  
Social services refer to an interconnected network of people who actively observe, report, collect, analyze, and disseminate information via text, audio, or video messages through smart devices. Social service is a combination of human-in-the-loop sensing, Web 2.0, and mobile computing [7]. In particular, Web 2.0 fostered the applications for tagging, blogging, wikis, and social networking sites that have made information consumption, production, and sharing incredibly easy. Recent significant developments in mobile computing facilitated the social services, such as the technology of Global Positioning System (GPS) and cameras on-board the mobile devices. Hence, the human sensor, _i.e._, social services should be an extensive data source for the PGIS.