BaseX 10
Draft, yet to be finalized
After 15 years of continuous development, the first double-digit version of BaseX is about to see the light of day soon.
We have taken the version jump as an opportunity to perform some major refactorings of BaseX, both under the hood and on API and XQuery level. Before migrating your projects to the new version, some adjustments may be required, so please read this article carefully.
Contents
Prerequisites
BaseX 10 requires Java 11 or later to run. Databases created with the new version are backward compatible and can still be opened with BaseX 9.
Migrating Applications
The following modifications might be relevant when migrating existing applications:
- The default ports for web applications have been changed from 8984/8985 to 8080/8081.
- If a new application of BaseX is deployed, the
admin
user can only be used after a custom password has been assigned, e.g., via thePASSWORD
command. - The conventions for functions in Clients in other programming languages were revised.
- The
IGNOREHOSTNAME
option was dropped and merged withIGNORECERT
.
Storage
Whitespaces
All whitespaces are now preserved when importing XML resources, unless whitespace stripping is enabled.
The notorious CHOP
option was removed to prevent conflicting behavior caused by earlier installations. It was replaced by a new STRIPWS
option, which defaults to false
. In addition, the new default of the serialization parameter indent
is no
.
Please be warned that the new default can throw off existing applications. If you want to restore the old behavior, you should assign the following values in your .basex configuration file, or the web.xml
file of your Web Application:
<syntaxhighlight lang="xquery"> STRIPWS: true SERIALIZER: indent=yes </syntaxhighlight>
In addition, databases may considerably increase in size, as whitespaces used for indenting an XML document will be interpreted and stored as additional text nodes. If your XML resources are structured and have no mixed content, it is advisable to enable whitespaces stripping when importing them to a database.
Value Resources
In addition to XML and binary resources, a third resource type has been added: XQuery values (atomic items and nodes, sequences, maps, arrays) can now be stored in databases as well. The db:put-value
and db:get-value
can be used to store to and retrieve values.
The new feature can e.g. be used to store maps in a database:
<syntaxhighlight lang="xquery"> db:put-value(
'factbook', map:merge( for $country in db:get('factbook')//country return map:entry($country/@name, $country//city/name ! string()) ), 'cities'
) </syntaxhighlight>
…and use them as index later on:
<syntaxhighlight lang="xquery"> let $cities := db:get-value('factbook', 'cities') for $country in ('Japan', 'Indonesia', 'Malaysia') return $country || ': ' || string-join($cities?($country), ', ') </syntaxhighlight>
Backups
The Backup Commands and Backup Functions were enhanced to back up general data: registered users, scheduled services, key-value stores.
XQuery
Compilation
Several internal steps are performed when a query is executed (see XQuery Optimizations for more details):
- The query is parsed, i.e., the original query string is transformed to an executable tree representation.
- External values that are passed on by APIs are bound to variables and the query context. External values can be names of databases, or contribute to a name that will later on be constructed in the query.
- The query is compiled and evaluated.
The transaction manager gathers the names of the databases that will be accessed by a query. If it is not possible to uniquely identify all databases that may be opened by the query, global locking will be applied and all databases will be locked. Detection can fail if the names of databases depend on external input. It can also fail if a query is too complex to associate character strings with database operations.
The compilation phase has now been split into two separate steps:
- Compilation of logical, context-independent operations. External values are bound to the query, and deterministic code is rewritten, simplified and pre-evaluated.
- Optimization of physical, context-based operations. Databases are opened and checked for available indexes; current date/time is retrieved. The resulting code is further rewritten and optimized.
Lock detection will be performed after the first step, and the code resulting from this step offers much more insight into which specific databases need to be locked. As a result, local locks can be applied to many more queries than before, and many queries can now run in parallel. An example:
<syntaxhighlight lang="xquery"> declare variable $n external; db:get('names-' || $n) </syntaxhighlight>
After the query has been parsed, a user-specific value (e.g., 123
) will be bound to $n
. The variable will be inlined by the compiler, and the argument of db:get
will be pre-evaluated to names123
. It is then easy for the lock detector to collect the name of the database that needs to read-locked before the query is eventually executed.
Another positive side effect of two-step compilation is that productive environments get faster in general: Queries can be compiled in parallel, and it’s only the optimization and evaluation of a query that may need to be delayed by locking.
Main-Memory Updates
XQuery Update provides constructs to update XML nodes in main memory. The data structures for in-memory representations of XML resources have been revised, such that updates can be performed orders of magnitudes faster than before. With BaseX 9.x, the following query runs for 6-7 minutes, whereas it can now be computed in 3 seconds:
<syntaxhighlight lang="xquery"> <xml>{
(1 to 1000000) ! <child/>
}</xml> update {
for $child at $pos in child return insert node text { $pos } into $child
} </syntaxhighlight>
Key-Value Store
A new Store Module provides functions to organize values in a persistent main-memory key-value store. The store allows you to speed up access to frequently accessed data.
- Store data
<syntaxhighlight lang="xquery"> let $email := map:merge(
for $address in db:get('addressbook')//address return map:entry($address/name, $address/email)
) return store:put('emails', $email) </syntaxhighlight>
- Retrieve data
<syntaxhighlight lang="xquery"> let $name := 'Richard David James' return store:get('email')($name) </syntaxhighlight>
The store is persistent: Its contents are written to disk, and retrieved from disk again after a restart.
Modules
Functions of all modules, excluding the File Module, now consistently resolve relative URI references against the static base URI, and not the current working directory.
Various modules and functions have been revised, added, renamed or removed:
Description | BaseX 10 | BaseX 9 |
---|---|---|
Retrieve XML resources | db:get
|
db:open
|
Retrieve nodes with specified pre values | db:get-pre
|
db:open-pre
|
Retrieve nodes with specified IDs | db:get-id
|
db:open-id
|
Retrieve binary resources | db:get-binary
|
db:retrieve
|
Retrieve value resources | db:get-value
|
new |
Add or replace resource | db:put , arguments swapped!
|
db:replace
|
Add or replace binary resource | db:put-binary , arguments swapped!
|
db:store
|
Add or replace value resource | db:put-value
|
new |
Get resource type | db:type
|
db:is-raw , db:is-xml
|
Fetch XML document | fetch:doc
|
fetch:xml
|
Convert binary data to XML | fetch:binary-doc
|
fetch:xml-binary
|
Module: Process Geo data | removed | Geo Module |
XQuery jobs | Job Module | Jobs Module |
Return variable bindings of a job | job:bindings
|
new |
Module: Main-memory key-value store | Store Module | new |
Module: String computations | String Module | Strings Module |
Format string | string:format
|
out:format
|
Return control characters | string:cr , string:nl , string:tab
|
out:cr , out:nl , out:tab
|
Module: Process ZIP files | removed | ZIP Module |
Commands
The following commands have been revised:
Description | BaseX 10 | BaseX 9 |
---|---|---|
Retrieve single XML document. | GET
|
– |
List directories and resources. | LIST
|
– |
Add or replace resources. | PUT
|
REPLACE
|
Store binary resource. | BINARY PUT
|
STORE
|
Retrieve binary resource. | BINARY GET
|
Old name: RETRIEVE
|
Returns the current option values. | SHOW OPTIONS
|
Old name: GET
|
HTTP Requests
HTTP requests in BaseX take advantage of the new Java HTTP Client. This client provides a better overall performance, uses internal connection pools and follows redirects across different protocols (http, https).
HTTP operations are, among others, performed by:
- the HTTP Client Module;
- the Fetch Module, Database Module, Fetch Module, Validation Module, XSLT Module or Repository Module;
fn:doc
andfn:collection
;- the
CREATE DB
andREPO INSTALL
commands.
REST
Results in the rest
namespace are now returned unprefixed:
<syntaxhighlight lang="xml"> <rest:databases xmlns:rest="http://basex.org/rest"/>
<databases xmlns="http://basex.org/rest"/> </syntaxhighlight>
When listing the resources of a database, dir
elements are returned for resources that are located in subdirectories.
Catalogs
From early on, catalog resolvers had been neglected both in BaseX and Java. This has changed: The new XML Catalog API from Java is universally used to resolve references to external resources. As an alternative, Norman Walsh’s Enhanced XML Resolver is utilized if it is found in the classpath.
The option for supplying the XML catalog was renamed from CATFILE
to CATALOG
. See Catalog Resolver for more details.
Graphical User Interface
The graphical user interface of BaseX has been revised and made more consistent.
The icons were replaced by scalable ones, building upon the HiDPI graphics support for Windows and Linux.