Changes

Jump to navigation Jump to search
5,124 bytes added ,  15:32, 27 February 2020
no edit summary
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 a unique database path. By defaultThere is no explicit layer for collections: Instead, collections are implicitly created and deleted, all resources have been and collections result from the existence of documents in specific paths. Resources can either be '''XML documents'''. Since {{Version|7.0}},however, or '''raw files''' (binaries) . Some information on [[Binary Data|binary data]] can be stored as wellfound on an 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. '''Note:''' A main-memory database will be created if the {{Option|MAINMEM}} option is enabled ([[Databases#In Memory Database|see below]] for more). =Access Resources= Stored resources and external documents can be accessed in different ways: ==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]|{{Code|collection("db/path/to/docs")}}|Returns all documents at the location {{Code|path/to/docs}} in the database {{Code|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 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: <syntaxhighlight lang="xquery">for $i in 1 to 100return db:open('books' || $i)//book/title</syntaxhighlight> If the {{Option|DEFAULTDB}} option is turned on, the path argument of the {{Code|fn:doc}} or {{Code|fn:collection}} function will first be resolved against the globally opened database. Two more functions are available for retrieving information on database nodes: {| class="wikitable"|-!Function!Example!Description|-|[[Database Module#db:name|db:name]]|{{Code|db:name($node)}}|Returns the name of the database in which the specified {{Code|$node}} is stored.|-|[[Database Module#db:path|db:path]]|{{Code|db:path($node)}}|Returns the path of the database document in which the specified {{Code|$node}} is stored.|} The {{Code|fn:document-uri}} and {{Code|fn:base-uri}} functions return URIs that can also be reused as arguments for the {{Code|fn:doc}} and {{Code|fn:collection}} functions. As a result, the following example query always returns {{Code|true}}: <syntaxhighlight lang="xquery">every $c in collection('anyDB')satisfies doc-available(document-uri($c))</syntaxhighlight> If the argument of {{Code|fn:doc}} or {{Code|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: * {{Code|doc("http://web.de")}}: retrieves the addressed URI and returns it as a main-memory document node.* {{Code|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.
Existing databases can eventually be dropped again:==Raw Files==
* The <code>[[StartupCommands#BaseX StandaloneRETRIEVE|ConsoleRETRIEVE]]: enter </code>basex -c "DROP DB dbname"command and the </code>.* [[StartupDatabase Module#BaseX GUIdb:retrieve|GUIdb:retrieve]]: Go </code> function can be used to ''Database'' → ''Manage'' and choose the database to be droppedreturn files in their native byte representation.
If the API you use does not support binary output (this is e.g. the case for various [[Clients|Client]] language bindings), you need to convert your binary data to its string representation before returning it to the client: <syntaxhighlight lang="xquery">string(db:retrieve('multimedia', 'sample.avi'))</syntaxhighlight> =Manage =HTTP Services== * With [[REST]] and [[WebDAV]], all database resources can be requested in a uniform way, no matter if they are well-formed XML documents or binary files. =Update Resources==
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>.
* Any resource Existing resources can be replaced with another using the <code>[[Commands#REPLACE|REPLACE]]</code> command.* Any resources Resources can be deleted with the via <code>[[Commands#DELETE|DELETE]]</code> commandThe {{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 and finally delete them again(to speed up the insertion of new documents in bulk operations, you can turn the [[Options#AUTOFLUSH|AUTOFLUSH]] option off):<presyntaxhighlight>
CREATE DB example
SET AUTOFLUSH offfalse
ADD example.xml
SET ADDCACHE trueADD .../path/to/xml/documents
STORE TO images/ 123.jpg
FLUSH
DELETE /
</presyntaxhighlight>
You may as well also use the BaseX-specific [[Database FunctionsModule|XQuery Database Functions]] to create, add, replace , and delete XML documents:
<pre classsyntaxhighlight lang="brush:xquery">for let $file in fileroot :list(= "/path/to/xml/documents/"for $file in file:list($root)return db:add("database", $root || $file)</presyntaxhighlight>
Last but not least, XML documents can also be added via the GUI and the ''Database'' menu.
=Export Data=Access Resources== All resources stored in a database can be ''exported'', i.e., written back to disk. This can be done in several ways: * Commands: <code>[[Commands#EXPORT|EXPORT]]</code> writes all resources to the specified target directory* 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
The stored resources can be accessed in different ways:=Main-Memory Database Instances=
====XML Documents====* 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>
Various XQuery functions exist '''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 access the XML documents in databases and other locations:those of main-memory database instances (no matter which value is set for {{Option|MAINMEM}}).
* <code>db:open("dbname", "path/to/docs")</code>: (only) returns documents that are found in the specified database.* <code>collection("path/to/docs")</code>: returns the documents that are either found in the database specified in the argument, or at the specified location (file path or URL).* <code>doc("path/to/document.xml")</code>: returns a single document found at the specified location (file path or URL). If a database already exists for the addressed resource, it is opened instead.=Changelog=
====Raw Files====;Version 8.4
* The <code>Updated: [[Commands#RETRIEVERaw Files|RETRIEVERaw Files]]: Items of binary type can be output without specifying the obsolete </code> command returns raw files without modifications.* The XQuery function <code>db:retrieve("dbname", "path/to/docs")</code> returns raw files in their Base64 representationserialization method. By choosing <code>"method=raw"</code> as [[Serialization|Serialization Option]], the data is returned in its raw form:
<pre class="brush:xquery">declare option output:method "raw";db:retrieve('multimedia', 'sampleVersion 7.avi')</pre>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.
Bureaucrats, editor, reviewer, Administrators
13,550

edits

Navigation menu