The semi-structured model is a

database model A database model is a type of data model that determines the logical structure of a database. It fundamentally determines in which manner data can be stored, organized and manipulated. The most popular example of a database model is the relationa ...

where there is no separation between the

data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...

and the

schema The word schema comes from the Greek word ('), which means ''shape'', or more generally, ''plan''. The plural is ('). In English, both ''schemas'' and ''schemata'' are used as plural forms. Schema may refer to: Science and technology * SCHEMA ...

, and the amount of structure used depends on the purpose. The advantages of this model are the following: * It can represent the information of some data sources that cannot be constrained by schema. * It provides a flexible format for data exchange between different types of databases. * It can be helpful to view structured data as semi-structured (for browsing purposes). * The schema can easily be changed. * The data transfer format may be portable. The primary trade-off being made in using a semi-structured

is that queries cannot be made as efficiently as in a more constrained structure, such as in the

relational model The relational model (RM) is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by English computer scientist Edgar F. Codd, where all data is represented in terms of tup ...

. Typically the records in a semi-structured database are stored with unique IDs that are referenced with pointers to their location on disk. This makes navigational or path-based queries quite efficient, but for doing searches over many records (as is typical in SQL), it is not as efficient because it has to seek around the disk following pointers. The Object Exchange Model (OEM) is one standard to express semi-structured data, another way is

XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. ...

See also