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In BaseX, a ''database'' is a pretty light-weight concept. It may contain one or more '''resources''', which are addressed by a unique database path. There is no explicit layer for collections: Instead, collections are implicitly created and deleted, and collections result from the existence of documents in specific paths. Resources can either be The resource types exist: '''XML documents''' or , '''raw filesBinary data''', and '''XQuery Values''' (binaries). Some Additional information on [[Binary Data|binary data]] can be found on an extra page.

Multiple databases can be addressed (queriesqueried, updated) with a single XQuery expression. As a single database is restricted to 2 billion XML nodes (see [[Statistics]]), resources can be distributed across multiple database instances.

Databases can be created via commands[[Commands]], via [[XQuery]], in the [[GUI]], or and with any of our various [[Developing|APIs]]. If an initial input is specified with a createoperation, some time can be saved, as the specified resources will be added to the database in a bulk operation:

* [[Startup#BaseX Standalone|Console]]: <code>CREATE DB db /path/to/resources</code> will add initial : Add documents in the specified path to a database.* [[Startup#BaseX GUI|GUI]]: Go to ''Database'' → ''New'', press ''BrowseBrowse…'' to choose an initial file or directory, and press ''OK''.

The name of a database is restricted to composed of a restricted set of characters (see [[Valid Names]]). Various [[parsers]] can be chosen selected to control the import process, or to convert different formats to XML.

'''Note:''' A database can be created in main-memory database will be created if by enabling the {{Option|MAINMEM}} option is enabled ([[Databases#In Memory Database|see below]] for moredetails).

==Binary FilesData==

The {{Command|RETRIEVEBINARY GET}} command and the {{Function|Database|db:get-binary}} function can be used to return files in their native byte representation.

If the API you use does not support binary output (this which is e.g. the case for various [[Clients|Client]] language bindings), you need to can convert your binary data to its string representation before returning it to the client:

==HTTP ServicesXQuery Values==

* With [[REST]] and [[WebDAV]]{{Function|Database|db:get-value}}, all database resources XQuery values can be requested retrieved. In the following example, we assume that an XQuery map {{Code|cities}} was stored in a uniform wayan {{Code|indexes}} database: <syntaxhighlight lang="xquery">let $city-map := db:get-value('indexes', no matter if they are well'cities')return $city-formed XML documents or binary files.map?Chile</syntaxhighlight>

* XML documents can be added with the {{Command|ADDPUT}} command.* Raw files are added with and {{Command|STOREADD}}commands.* Existing resources can be replaced Binary data is stored with the {{Command|BINARY PUT}} command.* Resources of all types can be deleted via {{Command|DELETE}}.

The {{Option|AUTOFLUSH}} option can be turned off before ''bulk operations'' (i.e. , before a large number of numerous new resources is are added to the database).

If {{Option|ADDCACHE}} is enabled, the input will be cached before it is added to the database. This is helpful when the input documents to be added are expected to consume too much main -memory.

The With the following commands create [[Commands#Command Scripts|command script]], an empty databaseis created, add two resourcesare added (one directly, explicitly flush data structures to diskanother one cached), and finally delete all inserted datais exported to the file system:

STORE BINARY PUT TO images/ 123.jpgFLUSHDELETE EXPORT /path/to/file-system/

==XQuery== You may can also use functions from the BaseX-specific [[Database Module|XQuery Database Functions]] to create, add, replace, and or delete XML documents:

let $root db:= "add('database', '/path/to/xml/documents/"for $file in file:list($root)return db:add("database", $root || $file')

Last but not leastFunction from other modules, such as the [[File Module]], XML documents can also be added via utilized to filter the input. With the GUI following code, all files that contain numbers in the filename are selected, and stored as XML. If an input file contains no well-formed XML, it is stored as binary resource, and the error message is stored as a string value: <syntaxhighlight lang="xquery">let $db := 'documents'Databaselet $root := '/path/to/documents/'for $path in file:list($root)where matches($path, '\d+')return try { db:put($db, fetch:doc($root || $path), $path)} catch * { db:put-binary($db, $root || $path, $path), db:put-value($db, $err:description, $path || ' menu.info')}</syntaxhighlight> The error messages can e.g. be analyzed in a second step: <syntaxhighlight lang="xquery">let $failures := db:get-value('misc')return map:for-each($failures, function($filename, $error) { $filename || ': ' || $error})</syntaxhighlight>

All resources stored in a database can be ''exported'', i.e., written back to disk, e. This can be done in several waysg., as follows:

* Commands: {{Command|EXPORT}} writes all resources to the specified target directory.* GUI: Go to ''Database'' → ''Export'', choose the target directory and press ''OK''.* XQuery: Use {{Function|Database|db:export}}.* WebDAV: Locate the database directory (or a subdirectory of it) and copy all contents to another location.

* You can force an ordinary database to being copied to memory by using applying an empty [[XQuery_Update#Main-Memory_Updates|main-memory update]] on a database node: <code>db:get('some-db') update {}</code>

'''Note:''' If you address a URI open local or remote documents with <code>fn:doc</code> or <code>fn:collection</code> for which no database exists, the resulting internal representation is identical to those of main-memory database instances (no matter regardless of which value is set for {{Option|MAINMEM}}).