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This page is part of the [[Getting Started]] Section.
In BaseX, a single ''database contains an arbitrary number of '' is a pretty light-weight concept. It may contain one or more '''resources''',which are addressed by their a unique database path. Since {{Version|7There is no explicit layer for collections: Instead, collections are implicitly created and deleted, and collections result from the existence of documents in specific paths.0}}, resources Resources caneither be '''XML documents''' or '''raw files''' (binaries). Sets of XML documentsare also called collections. Some information on [[Binary Data|binary data]] can be found onan extra page.
=Create/Drop Database=Multiple databases can be addressed (queries, updated) with a single XQuery expression. As a single database is restricted to 2 billion nodes (see [[Statistics]]), resources can be distributed across multiple database instances.
New databases can either be created in the GUI, on command line, or using any of our [[APIs]]. XML documents can be specified along with the create operation, which will be added to the database in a bulk operation:=Create Databases=
Databases can be created via commands, via XQuery, in the GUI, or with any of our [[Developing|APIs]]. If an initial input is specified with create, some time can be saved, as the specified resources will be added to the database in a bulk operation: * [[Startup#BaseX Standalone|Console]]: enter <code>basex -c "CREATE DB dbname db /path/to/resources"</code>will add initial documents to a database
* [[Startup#BaseX GUI|GUI]]: Go to ''Database'' → ''New'', press ''Browse'' to choose an initial file or directory, and press ''OK''
The name of a database is restricted to a restricted set of characters (see [[Valid Names]]). Various [[parsers]] can be chosen to influence control the database creationimport process, or to convert different formats to XML. Existing databases can eventually be dropped again: * [[Startup#BaseX Standalone|Console]]: enter <code>basex -c "DROP DB dbname"</code>.* [[Startup#BaseX GUI|GUI]]: Go to ''Database'' → ''Manage'' and choose the database to be dropped
Database must follow '''Note:''' A main-memory database will be created if the {{Option|MAINMEM}} option is enabled ([[Valid NamesDatabases#In Memory Database|valid names constraintssee below]]for more).
=Access Resources=
==XML Documents==
Various XQuery functions exist to access XML documents in databases: {| class="wikitable"|-!Function!Example!Description|-|[[Database Module#db:open|db:open]]|{{Code|db:open("db", "path/to/docs")}}|Returns all documents that are found in the database {{Code|db}} at the (optional) path {{Code|path/to/docs}}.|-|[http://www.xqueryfunctions.com/xq/fn_collection.html fn:collection]|{{MarkCode|Updated with Version 7collection("db/path/to/docs")}}|Returns all documents at the location {{Code|path/to/docs}} in the database {{Code|db}}.2<br/>If no path is specified after the database, all documents in the database will be returned.<br/>If no argument is specified, all documents of the database will be returned that has been opened in the global context.|-|[http://www.xqueryfunctions.com/xq/fn_doc.html fn:doc]|{{Code|doc("db/path/to/doc.xml")}}|Returns the document at the location {{Code|path/to/docs}} in the database {{Code|db}}.<br/>An error is raised if the specified yields zero or more than one document.|} You can access multiple databases in a single query: <pre class="brush:xquery">for $i in 1to 100return db:open('books' || $i)//book/title</pre> If the {{Option|DEFAULTDB}} option is turned on, the path argument of the {{Code|fn:doc}} or {{Code|fn:collection}}function will first be resolved against the globally opened database.
Various XQuery Two more functions exist to access XML documents in databases and from other locationsare available for retrieving information on database nodes:
{| class="wikitable"
!Description
|-
|<code>[[Database Module#db:openname|db:open()name]]</code>|{{MonoCode|db:openname("db", "path/to/tocs"$node)}}|Returns all documents that are found in the name of the database {{Mono|db}} at in which the (optional) path specified {{MonoCode|path/to/docs$node}}is stored.
|-
|<code>[http[Database Module#db://www.xqueryfunctions.com/xq/fn_collection.html fnpath|db:collection()path]]</code>|{{MonoCode|collection("db/:path/to/docs"($node)}}|Returns all documents at the location {{Mono|path/to/docs}} in the database {{Mono|db}}.<br/>If no path is specified after the database, all documents in the database will be returned.<br/>If no argument is specified, all documents of the currently opened database will be returned.|-|<code>[http://www.xqueryfunctions.com/xq/fn_doc.html fn:doc()]</code>|{{Mono|doc("db/path/to/doc.xml")}}|Returns the document at the location {{Mono|path/to/docs}} in which the database specified {{MonoCode|db$node}}.<br/>An error is raised if the specified addresses does not address exactly one documentstored.
|}
The {{MonoCode|fn:document-uri()}} and {{MonoCode|fn:base-uri()}} functions return URIs that can also be reused as arguments for the {{MonoCode|fn:doc()}} and {{MonoCode|fn:collection()}} functions. As a result of this, as an example, the following example query will always return returns {{MonoCode|true}}:
<pre class="brush:xquery">
</pre>
If the argument of {{MonoCode|fn:doc()}} or {{MonoCode|fn:collection()}} does not start with a valid database name, or if the addressed database does not exist, the string is interpreted as URI reference, and the documents found at this location will be returned. Examples:
* {{MonoCode|doc("http://web.de")}}: retrieves the addressed URI and returns it as a main-memory document node.* {{MonoCode|doc("myfile.xml")}}: retrieves the given file from the file system and returns it as a main-memory document node. Note that updates to main-memory nodes are not automatically written back to disk unless the {{Option|WRITEBACK}} option is set.* {{Code|collection("/path/to/docs")}}: returns a main-memory collection with all XML documents found at the addressed file path.
==Raw Files==
* XQuery: The <code>[[Commands#RETRIEVE|RETRIEVE]]</code> command and the <code>[[Database Module#db:retrieve("dbname", "path/to/docs")|db:retrieve]]</code> returns raw function can be used to return files in their Base64 native byte representation. By choosing <code>"method=raw"</code> as  If the API you use does not support binary output (this is e.g. the case for various [[SerializationClients|Serialization OptionClient]]language bindings), the you need to convert your binary data is returned in to its original byte string representationbefore returning it to the client:
<pre class="brush:xquery">
declare option output:method "raw";string(db:retrieve('multimedia', 'sample.avi'))
</pre>
 
* Commands: <code>[[Commands#RETRIEVE|RETRIEVE]]</code> returns raw files without modifications.
==HTTP Services==
Once you have created a database, additional commands exist to modify its contents:
 
* XML documents can be added with the <code>[[Commands#ADD|ADD]]</code> command.
* Raw files are added with <code>[[Commands#STORE|STORE]]</code>.
* Resource Existing resources can be replaced with other ones with the <code>[[Commands#REPLACE|REPLACE]]</code> command.
* Resources can be deleted via <code>[[Commands#DELETE|DELETE]]</code>.
The [[Options#AUTOFLUSH{{Option|AUTOFLUSH]] }} option can be turned off before ''bulk operations''(i.e. before a large number of new resources is 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 following commands create an empty database, add two resources, explicitly flush data structures to disk, and finally delete all inserted data:
The following commands create an empty database, add two resources, explicitly flush data
structures to disk, and finally delete all inserted data:
<pre>
CREATE DB example
SET AUTOFLUSH false
ADD example.xml
SET ADDCACHE trueADD .../path/to/xml/documents
STORE TO images/ 123.jpg
FLUSH
</pre>
You may as well also use the BaseX-specific [[Database Module|XQuery Database Functions]] to create, add, replace , and delete XML documents:
<pre class="brush:xquery">
* GUI: Go to ''Database'' → ''Export'', choose the target directory and press ''OK''
* WebDAV: Locate the database directory (or a sub-directory of it) and copy all contents to another location
 
=Main-Memory Database Instances=
 
* In the standalone context, a main-memory database can be created (using <code>CREATE DB</code>), which can then be accessed by subsequent commands.
* If a BaseX server instance is started, and if a database is created in its context (using <code>CREATE DB</code>), other BaseX client instances can access (and update) this database (using OPEN, db:open, etc.) as long as no other database is opened/created by the server.
* You can force an ordinary database to being copied to memory by using <code>db:open('some-db') update {}</code>
 
'''Note:''' If you address a URI 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 which value is set for {{Option|MAINMEM}}).
=Changelog=
===;Version 78.24 * Updated: [[#Raw Files|Raw Files]]: Items of binary type can be output without specifying the obsolete <code>raw</code> serialization method.1===
* Updated: {{Mono|fn:document-uri()}} and {{Mono|fn:base-uri()}} now return strings that can be reused with {{Mono|fn:doc()}} or {{Mono|fn:collection()}} to reopen the original document;Version 7.2.1
[[Category* Updated:Beginner]]{{Code|fn:document-uri}} and {{Code|fn:base-uri}} now return strings that can be reused with {{Code|fn:doc}} or {{Code|fn:collection}} to reopen the original document.
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