Location Dependent Query Processing
Published on Aug 15, 2016
The continuous development of wireless networks and mobile devices has motivated an intense research in mobile data services. The advances in wireless and mobile computing allow a mobile user to perform a wide range of applications once limited to non-mobile hard wired computing environments.
As the geographical position of a mobile user is becoming more tractable, users need to pull data which are related to their location, perhaps seeking
information about unfamiliar places or local lifestyle data. In these requests, a location attribute has to be identified in order to provide more efficient access to location dependent data, whose value is determined by the location to which it is related. Local yellow pages, local events, and weather information are some of the examples of these data. There are several methods to process these data
Location of an object or a person is its geographical position on the earth with respect to a reference point. This information can be characterized by using a number of different representations including latitude/longitude/altitude or street addresses, etc. and by giving granularity, accuracy and rate of change (velocity). With the technological advances in cellular communications and sensing appliances, location of people has become more realtime and tractable. Location representation may include timestamp information as it may be related to a moving object/person, and may be represented in various ways
Introduction of Location Dependent Query Processing
Location can be estimated by using deferent methodologies, and will become information as common as date information. Location Dependent Data (LDD) is defined as data whose value is determined by the location to which it is related. Local yellow pages, local events, hotel and restaurant information are some of the examples of these data. Location dependence in queries implies that the information asked is related to a location but the location is not explicitly known when the query is asked. For example, “What are the names and addresses of the restaurants within 5 miles?" asks to find the restaurants within 5 miles of the current position of the query issuer. In order to provide the answer to the query, first we have to know the location of the issuer.
Query can then be bound to this location. When we find out the issuer's location, the query becomes Location Aware since; this special location attribute is explicitly stated to be the issuer's location. A query including any location related attribute in its predicates is defined as a Location Aware Query (LAQ). Location Based Services are services which provide value-added information by considering the location of the mobile users in order to give them customized information.
Technologies for LBS :
Two types of technologies relevant to LBSs are considered
These are technologies which make LBSs possible. They are positioning techniques used to determine the location of a mobile device. Several positioning methods with differentprecision can be used. For example, the cell-id technique, also called Cell of Origin (COO) or Cell Global Identity (CGI), allows one to identify the cell in which a certain wireless device is located. This method takes advantage of the location data that a wireless infrastructure stores about the mobile devices it serves. However, the precision of cell-id is usually not enough for the purposes of existing LBSs, as cells in urban environments have a typical size between 500 m and 2 km.
Thus, there is a myriad of other methods to obtain the location of a mobile device, such as Cell Global Identity with Timing Advance (CGI+TA), Uplink Time of Arrival (UL-TOA) or (TOA), Angle of Arrival (AOA), Observed Time Difference (OTD) or Enhanced Observed Time Difference (EOTD), Global Positioning System (GPS), network- Assisted GPS (AGPS). There are also methods based on infrared/RFID, Ultra-Wideband etc
These are technologies which are complementary technologies that provide the contextual environment where LBSs can be implemented in a value-added fashion. Four facilitating technologies for LBS are identified:
The Wireless Access Protocol (WAP) - It enables the access to information from the Internet taking into account limitations of mobile devices such as processing power and display size. WAP is a facilitating technology as it allows the specification of semantic links between locations and information.
The General Packet Radio Service (GPRS) or 2.5-generation mobile technology (2.5G) - It is the successor to GSM, which uses circuit-based connections, and Supports packet-based connections instead. This minimizes the connection time and allows charging based on data volume instead of airtime.
The Universal Mobile Telecommunication System (UMTS) or third-generation mobile technology (3G) - It also uses packet-based connections, but it provides more bandwidth than GPRS. This could allow the delivery of enhanced content to the user, such as videos of facilities in nearby hotels