A persistence framework is middleware

Middleware

Middleware is computer software that connects software components or people and their applications. The software consists of a set of services that allows multiple processes running on one or more machines to interact...

 that assists and automates the storage of program data into database

Database

A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...

s, especially relational database

Relational database

A relational database is a database that conforms to relational model theory. The software used in a relational database is called a relational database management system . Colloquial use of the term "relational database" may refer to the RDBMS software, or the relational database itself...

s.
It acts as a layer of abstraction between the application and the database, typically bridging any conceptual differences between the two.

Many persistence frameworks are also object-relational mapping

Object-relational mapping

Object-relational mapping in computer software is a programming technique for converting data between incompatible type systems in object-oriented programming languages. This creates, in effect, a "virtual object database" that can be used from within the programming language...

 (ORM) tools (e.g. Hibernate, iBATIS

IBATIS

iBATIS is a persistence framework which automates the mapping between SQL databases and objects in Java, .NET, and Ruby on Rails. In Java, the objects are POJOs . The mappings are decoupled from the application logic by packaging the SQL statements in XML configuration files...

 SQL Maps, and Java Ultra-Lite Persistence). Such frameworks map the objects in the application domain to data that needs to be persisted in a database. The mappings can be defined using either XML

XML

Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....

 files or metadata

Metadata

The term metadata is an ambiguous term which is used for two fundamentally different concepts . Although the expression "data about data" is often used, it does not apply to both in the same way. Structural metadata, the design and specification of data structures, cannot be about data, because at...

annotations.