Recommended Free Tools
A data description language describes the structure of data: what its elements are and how they are organized or related. In database terminology, “data description language” overlaps with the more familiar “data definition language,” also abbreviated DDL. The exact meaning depends on the system: database schema languages, dataset metadata formats, and OpenDDL are distinct uses of similar terminology.
What does data description language mean?
In a database context, a data description language is a formal way to describe data structure rather than the stored records themselves. It can specify data elements or attributes, the logical organization of a database, relationships among records, and logical ways to access them. The Office québécois de la langue française defines the term as a language for describing the structure of data in a database, and lists “data definition language” and “DDL” among its English equivalents: Office québécois de la langue française terminology record.
In many introductory SQL and relational-database contexts, DDL is expanded as “data definition language.” OpenStax uses that term for commands that create or modify database-object structure. It contrasts DDL with data manipulation language (DML), which creates, updates, or deletes data: OpenStax: Data Definition Language.
What does database DDL describe?
Database DDL describes the logical design: the database objects and their structural relationships. The scope can vary by system, but it is useful to separate that logical description from the physical arrangement of data on storage devices.
#1 Best Overall
- Data elements: the attributes or properties that make up the data.
- Logical structure: how the database is organized.
- Relationships: how records or data elements relate to one another.
- Logical access methods: how the data can be accessed at the logical level.
A U.S. government report records a working definition that includes those elements and explicitly excludes DMCL, a separate language for mapping data to physical storage media and describing its physical location and organization: U.S. government report on data description language and DMCL. The distinction is that a logical schema says how the database is structured, while physical-storage description concerns where and how it is stored.
How are schema and subschema different?
In the historical CODASYL database model, a schema describes the database as a whole, while a subschema describes the portion relevant to a particular program. The handbook characterizes schema description as device-independent: it describes the database without specifying physical devices or media. These are terms from that database context, not universal labels used identically by every modern database system: CODASYL Data Base Task Group handbook.
Rank #2
Why can DDL refer to different things?
DDL is an abbreviation used by several systems and projects. The shared name does not mean that they use one universal syntax or describe the same kind of object.
| Usage | Domain and object described | How it relates to storage |
|---|---|---|
| Database data description or data definition language | Database objects, attributes, logical organization, and relationships; in SQL teaching, DDL defines or changes object structure. | Logical schema description is distinct from physical device or media mapping. Government report; OpenStax. |
| Berkeley SDA DDL | A metadata format for dataset-level characteristics and variables, including missing-data specifications and category labels. | Describes dataset metadata; it is not the database-language meaning. Berkeley’s documentation identifies SDA version 4.1 and says the format can be authored as text or generated with a converter. Berkeley SDA DDL documentation. |
| OpenDDL (Open Data Description Language) | A general-purpose, human-readable, strongly typed language for information exchange, originating with Open Game Engine Exchange and used in other applications. | A distinct structured-data language, not a database schema language. Its project site identifies specification version 3.0 and an update date of 25 October 2021. OpenDDL project site. |
How to tell which meaning applies
Use the surrounding context rather than the abbreviation alone. If the discussion is about SQL, tables, or database objects, DDL usually means the language used to define or alter database structure. If it concerns a study dataset and variable metadata, it may mean Berkeley SDA’s format. If it names OpenDDL or discusses general information exchange, it refers to the separate Open Data Description Language.
Quick Recap
Best Value
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
