What is a data access layer?

A data access layer (DAL) is a specific part of each computer program that facilitates access between the program and any type of persistent storage. Programs are any applications that run on your computer; persistent storage refers to any permanent storage location on your computer, such as hard drives. While running, programs are constantly writing and reading information to and from the hard drive. The role of the data access layer is to ensure that any program running on the system is able to get the information it needs as soon as it needs it.

Computer programs use a data access layer to access information on the hard drive.

As an intermediary or vendor in a business relationship, the data access layer sits between the program and the storage device. Every program running on the computer that needs to access information on the hard drive has functional data access layers. Instead of the main body of the program communicating directly with the persistent storage location, it delegates responsibility to the data access layer, which then acts on behalf of the program to perform the task. Its only “job” is to shuffle the information back and forth, freeing up the rest of the program to fulfill its other responsibilities.

A typical example of a functional data access layer involves a program that requires external information to operate; in other words, information that the program does not intuitively possess. For example, if a program is trying to calculate changes in a company’s profit margin over the last 10 years, it is unlikely that this information exists within the actual program. It will exist within a company’s financial records database, however. When the program realizes that it requires “Financial Statement X” or “Profit Report Y”, it tells the data access layer to find this information. The data access layer then extracts the necessary information from the appropriate database or table, returning it to the program so it can continue operating.

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Some programs that use a data access layer are database dependent; this means that they are designed to work with a specific type of database, limiting its transferability. Others are database agnostic, providing the ability to work with a wider range of database software. While it may seem that dependent data access layer programs are less useful, this is not necessarily the case. Because they are programmed to work with one type of database, they are likely to be more efficiently optimized, providing faster performance while working with the intended type of database system.

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