Database URI

This project proposes a standard for database connection URIs and provides a simple Perl implementation. This figure summarizes the definition syntax and for database URIs (illustration adapted from RFC 3986 --- STD 66, chapter 3):

  db:engine://username:[email protected]:8042/widgets.db?tz=utc&charset=utf8#users
  \/ \____/   \_______________/ \_________/ \__/ \________/ \/ \__/ \____/ \__/\____/
   |    |             |              |       |        |     |    |     |    |     |
   |    |         userinfo        hostname  port      |    key   |    key   |     |
   |    |     \________________________________/      |          |          |     |
   |    |                      |                      |        value      value   |
   |  engine                   |                      |     \_________________/   |
scheme  |                  authority         db name or path         |            |
 name   |     \___________________________________________/        query       fragment
   |    |                           |
   |    |                   hierarchical part
   |    |
   |    |      db name or path       query    fragment
   |  __|_   ________|________    _____|____  ____|____
  /\ /    \ /                 \  /          \/         \
  db:engine:my_big_fat_database?encoding=big5#log.animals

Notes on this syntax:

• The Database URI scheme is db. Consequently, database URIs always start with db:. This is the URI scheme that defines a database URI.

• Next comes the database engine. This part is a string naming the type of database engine for the database. It must always be followed by a colon, :. There is no formal list of supported engines, though certain implementations may specify engine-specific semantics, such as a default port.

• The authority part is separated from the engine by a double slash, //, and terminated by the next slash or end of the URI. It consists of an optional user-information part, terminated by @ (e.g., username:password@); a host address (e.g., domain name or IP address); and an optional port number, preceded by a colon, :.

• The path part specifies the database name or path. It must be separated from the authority, if the authority is present, by a single slash, /. If the database name is a full path, it may start with an additional slash.

• The optional query part, separated by a question mark, ?, contains key=value pairs separated by a semicolon, ;, or ampersand, &. These parameters may be used to configure a database connection with parameters not directly supported by the rest of the URI format.

• The optional fragment part, separted by a hash mark, #, contains additional context information, such as a table or view name.

Here are some database URIs without an authority part, which is typical for non-server engines such as SQLite, where the path part is a relative or absolute file name:

• db:sqlite:
• db:sqlite:foo.db
• db:sqlite:../foo.db
• db:sqlite:/var/db/foo.sqlite

Other engines may use a database name rather than a file name:

• db:ingres:mydb
• db:postgresql:template1

When a URI includes an authority part, it must be preceded by a double slash:

• db:postgresql://example.com/
• db:mysql://root@localhost/
• db:pg://postgres:[email protected]

Formally, the authority part requires a host name, but some implementations, inspired by the file scheme, might allow an empty host to imply localhost.

• db:mysql:/root@
• db:postgres://postgres:secr3t@
• db:sqlite:///

The path part contians the database name, separated from the authority by a single slash:

• db:postgresql://example.com/template1
• db:mongodb://localhost:27017/myDatabase
• db:oracle://scott:[email protected]/scott

Some databases, such as Firebird, take both a host name and a file path. Just put the relative or absolute path after that slash, as appropriate:

• db:firebird://localhost/test.gdb - Relative
• db:firebird://localhost/../test.gdb - Relative
• db:firebird://localhost/C:/temp/test.gdb - Absolute
• db:firebird://localhost/%2Ftmp/test.gdb - Absolute

Note the percent-encoded slash in the last example. Formally, an absolute path may not start with a slash, so we use its percent-encoded representation here. In practice, implementations may recognize a leading slash, anyway:

• db:firebird://localhost//tmp/test.gdb

Any URI format may optionally have a query part containing key/value pairs:

• db:sqlite:foo.db?foreign_keys=ON;journal_mode=WAL
• db:pg://localhost:5433/postgres?client_encoding=utf8;connect_timeout=10

URIs may also have a fragment that names a specific database object. Since database URIs will generally be used for connecting, this part may be ignored.

• db:sqlite:my.db#users
• db:pg://localhost/postgres#pg_catalog.pg_class.

URI Compliance

Formally, a database URI as defined here is an opaque URI starting with db: followed by an embedded server-style URI. For example, this database URI:

db:pg://localhost/mydb

Is formally the URI pg://localhost/mydb embedded in an opaque db: URI. It adheres to this formal definition because the scheme part of a URI is not allowed to contain a sub-scheme (or subprotocol, in the JDBC parlance). It is therefore a legal URI embedded in a second legal URI.

Informally, it's simpler to think of a database URI as a single URI starting with the combination of the scheme and the engine, e.g., db:pg.

Some may recognize URIs as database URIs in the absence of the db: scheme, provided their schemes correspond to widely-recognized database engines, such as postgresql, mysql, sqlite, mssql, and oracle. These are not formally recognized as standard schemes, though they may be recognized as standard engines by the db: scheme specification.

Inspiration

The format here is inspired by a lot of prior art.

• JDBC URIs set the precedent for an opaque URI with a second, embedded URI, as discussed here.

• A number of database URI formats set the standard for engine://authority/dbname, including:

  • PostgreSQL libpq URIs
  • SQLAlchemy URLs
  • Stackato database URLs
  • Django database URLs
  • Rails database URLs
  • Ruby Pg URL

Author

David E. Wheeler

Contributers

• Brian T. Wightman