Indexing, Query and Velocity-Constrained

Moving object environments are characterized by large 10 numbers of moving objects and numerous concurrent con11 tinuous queries over these objects. Efficient evaluation of 12 these queries in response to the movement of the objects is 13 critical for supporting acceptable response times. In such 14 environments the traditional approach of building an index 15 on the objects (data) suffers from the need for frequent 16 updates and thereby results in poor performance. In fact, 17 a brute force, no-index strategy yields better performance 18 in many cases. Neither the traditional approach, nor the 19 brute force strategy achieve reasonable query processing 20 times. The efficient and scalable evaluation of multiple 21 continuous queries on moving objects can be achieved by 22 leveraging two complimentary techniques: Query Indexing 23 and Velocity Constrained Indexing (VCI). Query Indexing 24 relies on i) incremental evaluation; ii) reversing the role 25 of queries and data; and iii) exploiting the relative loca26 tions of objects and queries. VCI takes advantage of the 27 maximum possible speed of objects in order to delay the 28 expensive operation of updating an index to reflect the 29 movement of objects. In contrast to techniques that require 30 exact knowledge about the movement of the objects, VCI 31 does not rely on such information. While Query Indexing 32 outperforms VCI, it does not efficiently handle the arrival 33 of new queries. Velocity constrained indexing, on the oth34 er hand, is unaffected by changes in queries. A combina35 tion of Query Indexing and Velocity Constrained Indexing 36 enables the scalable execution of insertion and deletion of 37 queries in addition to processing ongoing queries. 38