Semi-structured model
Encyclopedia
The semi-structured model is a database model
. In this model, there is no separation between the data and the schema, and the amount of structure used depends on the purpose.
The advantages of this model are the following:
The primary trade-off being made in using a semi-structured database model
is that queries cannot be made as efficient as in a more constrained structure, such as in the relational model
. 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
.
Database model
A database model is the theoretical foundation of a database and fundamentally determines in which manner data can be stored, organized, and manipulated in a database system. It thereby defines the infrastructure offered by a particular database system...
. In this model, there is no separation between the data and the 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 database model
Database model
A database model is the theoretical foundation of a database and fundamentally determines in which manner data can be stored, organized, and manipulated in a database system. It thereby defines the infrastructure offered by a particular database system...
is that queries cannot be made as efficient as in a more constrained structure, such as in the relational model
Relational model
The relational model for database management is a database model based on first-order predicate logic, first formulated and proposed in 1969 by Edgar F...
. 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
SQL
SQL is a programming language designed for managing data in relational database management systems ....
), it is not as efficient because it has to seek around the disk following pointers.
The Object Exchange Model
Object Exchange Model
The Object Exchange Model is a model for exchanging semi-structured data between object-oriented databases. It serves as the basic Data model in numerous projects of the Stanford University Database Group, including Tsimmis, Lore, and C3 ....
(OEM) is one standard to express semi-structured data, another way is 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....
.