Chapter 3. Introduction to data virtualization
A virtual database enables you to aggregate data from one or more external data sources and apply a custom schema to the data. By applying a customized logical schema to the aggregated source data, you can curate the data in a way that makes it easy for your applications to consume. The virtual view exposes just the data that you want from each data source, down to the level of specific tables, columns or procedures. Query processing logic in the virtual database enables users to access and join data in different formats from across data sources.
The virtual database provides an abstraction layer that shields client applications from the details of the physical data sources. Data consumers don’t have figure out how to connect to the host sources. They also don’t have to worry about how a view combines data from various sources, or how to configure translators to normalize data into a usable format.
Data and access where you want it
Data virtualization acts as a logical data warehouse, one that relies on metadata to make data available to client applications. Unlike data marts or physical data warehouses, data virtualization never moves or copies data from its original source. All data remains hosted in the original external data sources, and is retrieved directly, in real time from the source systems. So there’s no additional storage costs, and no overhead related to copying data. Because data is not duplicated or mirrored, there is never a concern about data currency or a need to reconcile conflicting snapshots.
The virtual database provides the single point of access to all of the configured data sources. Applications connect over standard protocols to communicate with the virtual database, and interact with it as though it were any relational database. You can use standard SQL to retrieve and manipulate data in the data sources, even when a data source does not offer native SQL support. SQL queries that you run against a virtual view span the data sources in the view so that all of the data is available to your applications.
Apply consistent, secure data access policies
Typically, data access policies can vary across multiple data sources. Users who want to fetch data from across those sources might require specific permissions to access each one, greatly complicating efforts to formulate queries that span the data set.
By virtualizing multiple sources into a single service, you simplify access management. A virtual database restricts access to your critical primary data sources to a single trusted service. Only the virtual database makes a direct connection to your configured data sources, reducing unwanted access to sensitive information. At the same time, through the data that you expose through virtual views, users obtain "pass-through" access to the information that they need to do their jobs.