Databases

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Revision as of 21:38, 13 January 2013

This page is part of the Getting Started Section.

In BaseX, a database is a pretty light-weight structure and can be compared with a collection. It contains an arbitrary number of resources, addressed by their unique database path. Resources can either be XML documents or raw files (binaries). Some information on binary data can be found on an extra page.

Contents

Create Databases

New databases can be created via commands, in the GUI, or with any of our APIs. If some input is specified along with the create operation, it will be added to the database in a bulk operation:

Database must follow the valid names constraints. Various parsers can be chosen to influence the database creation, or to convert different formats to XML.

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 and from other locations:

Function Example Description
db:open() db:open("db", "path/to/docs") 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:

Raw Files

declare option output:method "raw";
db:retrieve('multimedia', 'sample.avi')

HTTP Services

Update Resources

Once you have created a database, additional commands exist to modify its contents:

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:

Changelog

Version 7.2.1
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