A database management system (DBMS) usually performs query optimization based on statistical information about data in the underlying database. Out-of-date statistics may lead to inefficient query processing in the system. Existing solutions to this problem have some drawbacks such as heavy administrative burden, high system load, and tardy updates. To overcome these drawbacks, our new approach, called the piggyback method, is proposed in this paper. The key idea is to piggyback some additional retrievals during the processing of a user query in order to collect more up-to-date statistics. The collected statistics are used to optimize the processing of subsequent queries. To specify the piggybacked queries, basic piggybacking operators are defined in this paper. Using the operators, several types of piggybacking such as vertical, horizontal, mixed vertical and horizontal, and multi-query piggybacking are introduced. Statistics that can be obtained from different access methods...

The O-tree is an indexing mechanism closely related to B-trees and Prefix B-trees. In this paper we derive the expected storage overhead of O-Trees under the standard Bernoulli model of randomness, compare the results with the expected overhead of B-trees and Prefix B-trees under the same conditions, and assess the expected relative improvements.

A picture archiving and communication system (PACS) infratructure is the necessary framework to integrate distributed and #{149}eterogeneous imaging systems, provide intelligent data-base nanagement of all radiology-related information, arrange an eficient means of viewing, analyzing, and documenting study re-3u1t5, and furnish a mechanism for effectively communicating study results to the referring physician. The PACS infrastructure consists of a basic skeleton of hardware components integrated by standardized, flexible software subsystems. This review describes these concepts and basic building blocks drawn from our original investigation, past experience, and the current clinical system in our radiology department. A PICTURE ARCHIVING AND COMMUNICATION SYSTEM (PACS) has many definitions, depending on the user’s perspective. It can be as simple as a film digitizer connected to a display station and a small image data base, or it can be as complex as a total hospital image management system. Generally speaking, a PACS consists ofacquisition, storage, and display subsystems integrated by various digital networks. From 1 986 to 1 989, we designed three PACS modules that serviced a small subset of the total operations of the radiology department. These PACS modules were independently implemented within our institution in pediatric radiology [1], the coronary care unit [2], and neuroradiology [3]. The modules demon-