Difference between revisions of "Databases"

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|<code>[http://www.xqueryfunctions.com/xq/fn_collection.html fn:collection()]</code>
 
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|{{Mono|collection("db/path/to/docs")}}
 
|{{Mono|collection("db/path/to/docs")}}
|Returns all documents at the location {{Mono|path/to/docs}} in the database {{Mono|db}}.<br/>All documents in the database will be returned if no path is specified.
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|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.
 
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|<code>[http://www.xqueryfunctions.com/xq/fn_doc.html fn:doc()]</code>
 
|<code>[http://www.xqueryfunctions.com/xq/fn_doc.html fn:doc()]</code>

Revision as of 00:28, 26 April 2012

This page is part of the Getting Started Section.

In BaseX, a single database contains an arbitrary number of resources, addressed by their unique database path. Since Version 7.0, resources can either be XML documents or raw files (binaries). Sets of XML documents are also called collections. Some information on binary data can be found on an extra page.

Create/Drop Database

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:

  • Console: enter basex -c "CREATE DB dbname /path/to/resources"
  • GUI: Go to DatabaseNew, press Browse to choose an initial file or directory, and press OK

Various parsers can be chosen to influence the database creation, or to convert different formats to XML.

Existing databases can eventually be dropped again:

  • Console: enter basex -c "DROP DB dbname".
  • GUI: Go to DatabaseManage and choose the database to be dropped

Database must follow the valid names constraints.

Access Resources

Stored resources and external documents can be accessed in different ways:

XML Documents

Updated with Version 7.2.1:

Various XQuery functions exist to access XML documents in databases and from other locations:

Function Example Description
db:open() db:open("db", "path/to/tocs") Returns all documents that are found in the database db at the (optional) path path/to/docs.
fn:collection() collection("db/path/to/docs") Returns all documents at the location path/to/docs in the database db.
If no path is specified after the database, all documents in the database will be returned.
If no argument is specified, all documents of the currently opened database will be returned.
fn:doc() doc("db/path/to/doc.xml") Returns the document at the location path/to/docs in the database db.
An error is raised if the specified addresses does not address exactly one document.

The fn:document-uri() and fn:base-uri() functions return URIs that can be reused as arguments for the fn:doc() and fn:collection() functions. As a result of this, as an example, the following query will always return true:

every $c in collection('anyDB')
satisfies doc-available(document-uri($c))

If the argument of fn:doc() or 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:

  • doc("http://web.de"): retrieves the addressed URI and returns it as a main-memory document node.
  • collection("/path/to/docs"): returns a main-memory collection with all XML documents found at the addressed file path.

Raw Files

  • XQuery: db:retrieve("dbname", "path/to/docs") returns raw files in their Base64 representation. By choosing "method=raw" as Serialization Option, the data is returned in its original byte representation:
declare option output:method "raw";
db:retrieve('multimedia', 'sample.avi')
  • Commands: RETRIEVE returns raw files without modifications.

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 ADD command.
  • Raw files are added with STORE.
  • Resource can be replaced with other ones with the REPLACE command.
  • Resources can be deleted via DELETE.

The AUTOFLUSH option can be turned off before bulk operations (i.e. before a large number of new resources is added to the database).

The following commands create an empty database, add two resources, explicitly flush data structures to disk, and finally delete all inserted data:

CREATE DB example
SET AUTOFLUSH false
ADD example.xml
ADD ...
STORE TO images/ 123.jpg
FLUSH
DELETE /

You may as well use the BaseX-specific XQuery Database Functions to add, replace and delete XML documents:

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

Last but not least, XML documents can also be added via the GUI and the Database menu.

Export Data

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

  • Commands: EXPORT writes all resources to the specified target directory
  • GUI: Go to DatabaseExport, 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

Changelog

Version 7.2.1

  • Updated: fn:document-uri() and fn:base-uri() now return strings that can be reused with fn:doc() or fn:collection() to reopen the original document.