The problem of answering queries using views is to find efficient methods of answering a query using a set of previously defined materialized views over the database, rather than accessing the database relations. The problem has recently received significant attention because of its relevance to a wide variety of data management problems. In query optimization, finding a rewriting of a query using a set of materialized views can yield a more efficient query execution plan. To support the separation of the logical and physical views of data, a storage schema can be described using views over the logical schema. As a result, finding a query execution plan that accesses the storage amounts to solving the problem of answering queries using views. Finally, the problem arises in data integration systems, where data sources can be described as precomputed views over a mediated schema. This article surveys the state of the art on the problem of answering queries using views, and synthesizes the disparate works into a coherent framework. We describe the different applications of the problem, the algorithms proposed to solve it and the relevant theoretical results.

/pdf/answering-queries-using-views-a-survey-4aug5icc6d.pdf

Answering queries using views: A survey

Distributed data processing is becoming a reality. Businesses want to do it for many reasons, and they often must do it in order to stay competitive. While much of the infrastructure for distributed data processing is already there (e.g., modern network technology), a number of issues make distributed data processing still a complex undertaking: (1) distributed systems can become very large, involving thousands of heterogeneous sites including PCs and mainframe server machines; (2) the state of a distributed system changes rapidly because the load of sites varies over time and new sites are added to the system; (3) legacy systems need to be integrated—such legacy systems usually have not been designed for distributed data processing and now need to interact with other (modern) systems in a distributed environment. This paper presents the state of the art of query processing for distributed database and information systems. The paper presents the “textbook” architecture for distributed query processing and a series of techniques that are particularly useful for distributed database systems. These techniques include special join techniques, techniques to exploit intraquery paralleli sm, techniques to reduce communication costs, and techniques to exploit caching and replication of data. Furthermore, the paper discusses different kinds of distributed systems such as client-server, middleware (multitier), and heterogeneous database systems, and shows how query processing works in these systems.

/pdf/the-state-of-the-art-in-distributed-query-processing-2b23xet25f.pdf

The state of the art in distributed query processing

We propose a semantic model for client-side caching and replacement in a client-server database system and compare this approach to page caching and tuple caching strategies. Our caching model is based on, and derives its advantages from, three key ideas. First, the client maintains a semantic description of the data in its cache,which allows for a compact specification, as a remainder query, of the tuples needed to answer a query that are not available in the cache. Second, usage information for replacement policies is maintained in an adaptive fashion for semantic regions, which are associated with collections of tuples. This avoids the high overheads of tuple caching and, unlike page caching, is insensitive to bad clustering. Third, maintaining a semantic description of cached data enables the use of sophisticated value functions that incorporate semantic notions of locality, not just LRU or MRU, for cache replacement. We validate these ideas with a detailed performance study that includes traditional workloads as well as a workload motivated by a mobile navigation application.

/pdf/semantic-data-caching-and-replacement-48oskamm93.pdf

Semantic Data Caching and Replacement

Location-dependent applications are becoming very popular in mobile environments. To improve system performance and facilitate disconnection, caching is crucial to such applications. In this paper, a semantic caching scheme is used to access location dependent data in mobile computing. We first develop a mobility model to represent the moving behaviors of mobile users and formally define location dependent queries. We then investigate query processing and cache management strategies. The performance of the semantic caching scheme and its replacement strategy FAR is evaluated through a simulation study. Our results show that semantic caching is more flexible and effective for use in LDD applications than page caching, whose performance is quite sensitive to the database physical organization. We also notice that the semantic cache replacement strategy FAR, which utilizes the semantic locality in terms of locations, performs robustly under different kinds of workloads.

http://people.cs.aau.dk/~simas/teaching/map_download/p210-ren.pdf

Using semantic caching to manage location dependent data in mobile computing

Current commercial databases allow application programmers to trade off consistency for performance. However, existing definitions of weak consistency levels are either imprecise or they disallow efficient implementation techniques such as optimism. Ruling out these techniques is especially unfortunate because commercial databases support optimistic mechanisms. Furthermore, optimism is likely to be the implementation technique of choice in the geographically distributed and mobile systems of the future. This thesis presents the first implementation-independent specifications of existing ANSI isolation levels and a number of levels that are widely used in commercial systems, e.g., Cursor Stability, Snapshot Isolation. It also specifies a variety of guarantees for predicate-based operations in an implementation-independent manner. Two new levels are defined that provide useful consistency guarantees to application writers; one is the weakest level that ensures consistent reads, while the other captures some useful consistency properties provided by pessimistic implementations. We use a graph-based approach to define different isolation levels in a simple and intuitive manner. The thesis describes new implementation techniques for supporting different weak consistency levels in distributed client-server environments. The mechanisms are based on optimism and make use of multipart timestamps. A new technique is presented that allows multipart timestamps to scale well with the number of clients and servers in our system; the technique takes advantage of loosely synchronized clocks for removing old information in multipart timestamps. This thesis also presents the results of a simulation study to evaluate the performance of our optimistic schemes in data-shipping client-server systems The results show that the cost of providing serializability relative to mechanisms that provide lower consistency guarantees is negligible for low-contention workloads; furthermore, even for workloads with moderate to high-contention workloads, the cost of serializability is low. The simulation study also shows that our mechanisms based on multipart timestamps impose very low CPU, memory, and network costs while providing strong consistency guarantees to read-only and executing transactions. Thesis Supervisor: Barbara H. Liskov Title: Ford Professor of Engineering

/pdf/weak-consistency-a-generalized-theory-and-optimistic-3acnuqje8k.pdf

Weak Consistency: A Generalized Theory and Optimistic Implementations for Distributed Transactions

We propose a new client-side data-caching scheme for relational databases with a central server and multiple clients. Data are loaded into each client cache based on queries executed on the central database at the server. These queries are used to form predicates that describe the cache contents. A subsequent query at the client may be satisfied in its local cache if we can determine that the query result is entirely contained in the cache. This issue is called cache completeness. A separate issue, cache currency, deals with the effect on client caches of updates committed at the central database. We examine the various performance tradeoffs and optimization issues involved in addressing the questions of cache currency and completeness using predicate descriptions and suggest solutions that promote good dynamic behavior. Lower query-response times, reduced message traffic, higher server throughput, and better scalability are some of the expected benefits of our approach over commonly used relational server-side and object ID-based or page-based client-side caching.

/pdf/a-predicate-based-caching-scheme-for-client-server-database-59rgoi5sqd.pdf

A predicate-based caching scheme for client-server database architectures

We propose a new client-side data caching scheme for relational databases with a central server and multiple clients. Data is loaded into a client cache based on queries, which are used to form predicates describing the cache contents. A subsequent query at the client may be satisfied in its local cache if we can determine that the query result is entirely contained in the cache. This issue is called 'cache completeness'. On the other hand, 'cache currency deals with the effect of updates at the central database on the client caches. We examine various performance and optimization issues involved in addressing the questions of cache currency and completeness using predicate descriptions. Expected benefits of our approach over commonly used object 1D-based caching include lower query response times, reduced message traffic, higher server throughput, and better scalability. >

/pdf/a-predicate-based-caching-scheme-for-client-server-database-595mx16p8s.pdf

A caching scheme that uses query predicates to cache data on the client-side in a client-server relational database system was presented in [15]. The client-side cache (henceforth referred to as a SQL*Cacheloads query results dynamically in the course of transaction execution, and formulates a cache description based on the query predicates. SQL*Cache is associative in nature, in that it supports content-based reasoning and local execution of SQL queries on the cached data, thereby attempting to reduce query response times and increase server throughput. Local caching involves cache consistency maintenance and complicates transaction concurrency control -- in this paper, we examine serializability questions that arise in such a system. We first analyze the issues in supporting different (0/1/2/3) degrees of isolation that client transactions may specify, and describe algorithms to achieve these isolation levels. Then, we propose new levels of isolation that take into account the distributed nature of transaction execution, in terms of the lag of locally cached data with respect to the server database and discrepancies between local and remote reads. The SQL*Cache scheme is currently being implemented using a main memory database as the client-side cache, and commercial database servers as the backends.

Degrees of Transaction Isolation in SQL*Cache: A Predicate-based Client-side Caching System

A new language concept for high-level distributed programming is proposed. Programs are organised as a collection of concurrently executing processes. Some of these processes, referred to as liaison processes, have a monitor-like structure and contain ports which may be invoked by other processes for the purposes of synchronisation and communication. Synchronisation is achieved by conditional activation of ports and also through port control constructs which may directly specify the execution ordering of ports. These constructs implement a path-expression-like mechanism for synchronisation and are also equipped with options to provide conditional, non-deterministic and priority ordering of ports. The usefulness and expressive power of the proposed concepts are illustrated through solutions of several representative programming problems. Some implementation issues are also considered.

/pdf/ordered-ports-a-language-concept-for-high-level-distributed-14e2ymksvl.pdf

Ordered ports—a language concept for high-level distributed programming

Existing data-flow languages are incapable of supporting large, manageable and reliable non-deterministic programs. Operating system implementations and real-time applications require high-level non-deterministic programming facilities. Hoare's Communicating Sequential Processes and Brinch Hansen's Distributed Processes are two widely acclaimed distributed programming languages for conventional distributed computing systems. The powerful constructs of interprocess communication and synchronisation supported by the above two languages have been incorporated in Communicating Data Flow Channels (CDFC), and Distributed Data Flow Channels (DDFC), two languages proposed in this paper for distributed processing in data-flow systems. Several new features have been incorporated in these languages to make their execution more efficient in a data-flow environment. The implementation of these two languages on an abstract data-flow machine is investigated in detail. Two simulators have been implemented for testing the effectiveness of our implementation schemes for these two data-flow languages. These simulators are written in Pascal and run on a DEC 1090 computing system. This work demonstrates that a data-flow computing system can accommodate, without taking resort to specialised hardware units, the non-deterministic and synchronisation constructs of conventional languages with the attendant benefits of parallel data-driven execution.

/pdf/two-tools-for-interprocess-communication-in-distributed-data-35io9xp7d9.pdf

Two Tools for Interprocess Communication in Distributed Data-Flow Systems

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Julie Basu

Author Tools

Chat about Author

Papers

A predicate-based caching scheme for client-server database architectures

A predicate-based caching scheme for client-server database architectures

Degrees of Transaction Isolation in SQL*Cache: A Predicate-based Client-side Caching System

Ordered ports—a language concept for high-level distributed programming

Two Tools for Interprocess Communication in Distributed Data-Flow Systems