Incremental View Maintenance for Mobile Databases

Abstract

In a mobile environment, querying a database at a stationary server from a mobile client is expensive due to the limited bandwidth of a wireless channel and the instability of the wireless network. We address this problem by maintaining a materialized view in a mobile client's local storage. Such a materialized view can be considered as a data warehouse. The materialized view contains results of common queries in which the mobile client is interested. In this paper, we address the view update problem for maintaining the consistency between a materialized view at a mobile client and the database server. The content of a materialized view could become incoherent with that at the database server when the content of the database server and/or when the location of the client is changed. Existing view update mechanisms are 'push-based'. The server is responsible for notifying all clients whose views might be affected by the changes in database or the mobility of the client. This is not appropriate in a mobile environment due to the frequent wireless channel disconnection. Furthermore, it is not easy for a server to keep track of client movements to update individual client location-dependent views. We propose a 'pull-based' approach that allows a materialized view to be updated at a client in an incremental manner, requiring a client to request changes to its view from the server. We demonstrate the feasibility of our approach with experimental results.

Advances in Mobile Commerce Technologies

“…The querying need can be resolved by adding a geographical information system component to the database server (Choy, Kwan, and Leong, 2000) to enable geo-referencing. The relevant portion of the location-enriched database for a mobile client can be modeled as a view to that client (Lee, Leong, and Si, 2000a).…”

“…Since location-dependent queries form a significant portion of m-commerce services, mechanisms to improve the performance of location-dependent queries should be implemented (Madria et al, 2000). For instance, typical information that is useful with respect to a location can be materialized in the form of a data warehouse, whose content can be updated dynamically with respect to changes in location (Lee, Leong, & Si, 2000a). In particular, the client view is defined based on a conjunction of location-independent and location-dependent predicates.…”

Incremental update to aggregated information for data warehouses over Internet

“…A w arehouseand its aggregated data may be recomputed from scratch on demand, but the cost of recomputation can often be expensive. Since the degree of modi cation to base tables or relations is normally small, incremental maintenance techniques can be applied to deduce the c hanges to the views due to delta changes in data source 5,8].…”

Um modelo para manutenção de esquema e de dados em data warehouses implementados em plataformas móveis.

“…sugerem que o modelo tradicional de Data Warehouses, representado na Figura 1, precisa ser adaptado para um ambiente em que os consumidores de informação e até, eventualmente, os produtores estejam em plataformas móveis.ConformeLee; Si e Va Leong (2000), um ambiente móvel difere de um ambiente convencional cliente-servidor principalmente em dois aspectos. Primeiro, a comunicação entre o cliente móvel e o servidor é realizada, normalmente, por meio de canais de rede sem fio.…”

“…Estas características geram alto custo no acesso e consultas à base de dados do servidor, a partir de um ambiente móvel. Assim,(LEE; propõe manter visões materializadas do Data Warehouse localmente armazenadas na plataforma móvel. Estas visões materializadas podem manter apenas as informações necessárias às análises do cliente móvel, reduzindo a dependência de acesso constante ao servidor.Com base nesta proposta, o ambiente de Data Warehouse (ou data marts 2 ) em plataformas móveis pode também ser visto como um conjunto de visões materializadas do Data Warehouse, da mesma forma que o modelo de Data Warehouse tradicional conectado é visto como um conjunto de visões materializadas das fontes de informação.…”