5. Egocentric Spatial Query Re-write Rules

The egocentric ADTs that incorporate attributes relating to the user’s spatial reference frame were introduced in Chapter 4, which allows for different types of here and there queries. While the egocentric ADTs support here and there queries at a high conceptual level in an extended SQL syntax, it is necessary to transfer such user queries into executable statements. For example, the keyword “here” needs to trigger a measurement from a position sensor (e.g., a GPS receiver) such that the observed x- and y- coordinates get integrated into the query. Likewise, the sensor’s measurement accuracy must be considered in order to generate a reasonable answer. This process of transforming a user query into an executable statement is called query re-writing. Using this approach the queries can be processed against different types of spatial data sets and the query’s response is at a reasonable level of granularity.

Query re-writing is necessary in order to take the burden of knowing details about how to process the actual queries away from the user. It avoids having the user explicitly dealing with the sensors accuracies and minimizes otherwise cumbersome dialogues between user and system to determine desired levels of detail. The re-write does not completely eliminate the dialogue between user and system, however. For example, if a user asks the system “Where am I?” and the system responds “on the Earth,” the user would become annoyed.  The goal of this chapter is to develop a mechanism that allows the system to provide responses at the most detailed level that can be accurately discerned from the sensors.

5.1. Re-Writing Here Queries

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5.2. Re-Writing Here+ Queries

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5.3. Re-Writing There Queries

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5.4. Re-Writing There+ Queries

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5.5. Hypothesis Confirmation

The goal of this research is to seamlessly integrate the user’s perspective into the query language of a mobile GIS. The Hypothesis is supported by because the measurements from position and orientation sensors are sufficient to formulate executable spatial queries about “here” and “there”. The queries re-write rules demonstrated in this chapter show how database ADTs, which store data about the user time-of query position and orientation can be used to process SQL queries where the terms “here” and “there” are used. These re-write rules therefore allow a database management system to process the egocentric perspective that users have of their surroundings.

5.6. Summary

The egocentric spatial data model incorporates two kinds of egocentric spatial queries, relating to the user’s concept of here and there. In this chapter, the here and there queries are re-written so that they can incorporate different kinds of spatial data sets. Such query re-writing is necessary in order to relieve the user of the cognitive load of knowing the details regarding how to process the actual query. This query re-write avoids the necessity of a user dealing explicitly with sensor accuracies, and to minimize otherwise cumbersome dialogues between user and system to determine desired levels of detail.