What is a Data Warehouse?

A data warehouse is a place where data is stored for archival purposes, analysis purposes and security purposes. Usually a data warehouse is either a single computer or many computers (servers) tied together to create one giant computer system.


Data can consist of raw data or formatted data and can be on various types of topics including an organization's sales, salaries, operational data, summaries of data including reports, copies of data, human resource data, inventory data, external data to provide simulations and analysis, etc.

Besides being a store house for large amounts of data, they must possess systems in place that make it easy to access the data and use it in day to day operations. A data warehouse is sometimes said to be a major part in a decision support system. A way for an organization to use data to come up with facts, trends or relationships that can help them make effective decisions or create effective strategies to accomplish their goals.

There are many different models of data warehouses including Online Transaction Processing which is a warehouse built for speed and ease of use. Another type of data warehouse is called Online Analytical processing, this type of warehouse is more difficult to use and adds an extra step of analysis within the data. Usually it requires more steps which slows the process down and much more data in order to analyze certain queries.

In addition to this model, one of the more common data warehouse models include a data warehouse that is subject oriented, time variant, non volatile and integrated. Subject oriented means that data is linked together and is organized by relationships.

Time variant means that any data that is changed in the data warehouse can be tracked. Usually all changes to data are stamped with a time date and with a before and after value, so that you can show the changes through out a period of time.

Non volatile means that data is never deleted or erased. This is a great way to protect your most crucial data. Because this data is retained, you can continue to use it in a later analysis. Finally, the data is integrated, which means that a data warehouse uses data that is organizational wide instead of from just one department.

Besides the term data warehouse, a term that is frequently used is a data mart, data marts are smaller, less integrated data housings. They might be just a database on human resources records or sales data on just one division.

With improvements in technology, as well as innovations in using data warehousing techniques, data warehouses have changed from Offline Operational Databases to include an Online Integrated data warehouse.

Offline Operational Data Warehouses are data warehouses where data is usually copied and pasted from real time data networks into an offline system where it can be used. It is usually the simplest and less technical type of data warehouse.

Offline Data Warehouses are data warehouses that are updated frequently either daily, weekly or monthly and that data is then stored in an integrated structure, where others can access it and perform reporting.

Real Time Data Warehouses are data warehouses where it is updated each moment with the influx of new data. For instance, a Real Time Data Warehouse might incorporate data from a Point of Sales system and is updated with each sale that is made.

Integrated Data Warehouses are data warehouses that can be used for other systems to access them for operational systems. Some Integrated Data Warehouses are used by other data warehouses, allowing them to access them to process reports, as well as look up current data.

So why should you or your organization use a Data Warehouse? Here are some of the pros and cons of using this type of structure for data.

The number one reason why you should implement a data warehouse is so that employees or end users can access the data warehouse and use the data for reports, analysis and decision making. Using the data in a warehouse can help you locate trends, focus on relationships and help you understand more about the environment that your business operates in.

Data warehouses also increase the consistency of the data and allows it to be checked over and over to determine how relevant it is. Because most data warehouses are integrated, you can pull data from many different areas of your business, for instance human resources, finance, IT, accounting, etc.

While there are plenty of reasons why you should have a data warehouse, it should be noted that there are a few negatives of having a data warehouse including the fact that it is time consuming to create and to keep operating.

You might also have a problem with current systems being incompatible with your data. It is also important to consider future equipment and software upgrades; these may also need to be compatible with you data.

Finally, security might be a huge concern, especially if your data is accessible over an open network such as the internet. You do not want your data to be viewed by your competitor or worse hacked and destroyed.