学海无涯——数据仓库概要

工作中用到的数据库不少，对我而言，数据库就是“数据仓库”。但严格来讲，什么才是数据仓库呢？

---------------------------------------------------------------------------------------------------------------------------------------------------------------

数据仓库是决策支持系统（dss）和联机分析应用数据源的结构化数据环境。数据仓库研究和解决从数据库中获取信息的问题。数据仓库的特征在于面向主题、集成性、稳定性和时变性。
数据仓库 ，由数据仓库之父比尔·恩门（Bill Inmon）于1990年提出，主要功能仍是将组织透过资讯系统之联机事务处理(OLTP)经年累月所累积的大量资料，透过数据仓库理论所特有的资料储存架构，作一有系统的分析整理，以利各种分析方法如联机分析处理(OLAP)、数据挖掘(Data Mining)之进行，并进而支持如决策支持系统(DSS)、主管资讯系统(EIS)之创建，帮助决策者能快速有效的自大量资料中，分析出有价值的资讯，以利决策拟定及快速回应外在环境变动，帮助建构商业智能(BI)。
数据仓库之父比尔·恩门（Bill Inmon）在1991年出版的“Building the Data Warehouse”（《建立数据仓库》）一书中所提出的定义被广泛接受——数据仓库（Data Warehouse）是一个面向主题的（Subject Oriented）、集成的（Integrated）、相对稳定的（Non-Volatile）、反映历史变化（Time Variant）的数据集合，用于支持管理决策(Decision Making Support)。

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------

In computing, a data warehouse (DW or DWH), also known as an enterprise data warehouse (EDW), is a system used for reporting and data analysis, and is considered a core component of business intelligence. DWs are central repositories of integrated data from one or more disparate sources. They store current and historical data in one single place that are used for creating analytical reports for workers throughout the enterprise.

The data stored in the warehouse is uploaded from the operational systems (such as marketing or sales). The data may pass through an operational data store and may require data cleansing for additional operations to ensure data quality before it is used in the DW for reporting.

The typical Extract, transform, load (ETL)-based data warehouse uses staging, data integration, and access layers to house its key functions. The staging layer or staging database stores raw data extracted from each of the disparate source data systems. The integration layer integrates the disparate data sets by transforming the data from the staging layer often storing this transformed data in an operational data store (ODS) database. The integrated data are then moved to yet another database, often called the data warehouse database, where the data is arranged into hierarchical groups, often called dimensions, and into facts and aggregate facts. The combination of facts and dimensions is sometimes called a star schema. The access layer helps users retrieve data.

The main source of the data is cleansed, transformed, catalogued, and made available for use by managers and other business professionals for data mining, online analytical processing, market research and decision support. However, the means to retrieve and analyze data, to extract, transform, and load data, and to manage the data dictionary are also considered essential components of a data warehousing system. Many references to data warehousing use this broader context. Thus, an expanded definition for data warehousing includes business intelligence tools, tools to extract, transform, and load data into the repository, and tools to manage and retrieve metadata.