Status of this Document
This section describes the status of this document at the
time of its publication. Other documents may supersede this
document. A list of current W3C publications and the latest
revision of this technical report can be found in the W3C technical reports index at
http://www.w3.org/TR/.
W3C publishes a Candidate
Recommendation, as described in the Process
Document, to indicate that the document is believed to be
stable and to encourage implementation by the developer community.
The publication of this document constitutes a call for
implementations of this specification.
This document has been developed by the W3C XML Query Working Group, which is
part of the XML
Activity. It will remain a Candidate Recommendation until at
least 20 June 2008. The Working Group expects to eventually publish
this document as a Working Group Note.
The XML Query Working
Group intends to submit this document for consideration as a
W3C Proposed
Recommendation at the same time that XQuery Update Facility 1.0
is submitted for the same consideration.
Once the entrance criteria for Proposed Recommendation have been
achieved, the Director will be requested to advance this document
to Proposed
Recommendation status. Working closely with the developer
community, we expect to show evidence of implementations by
approximately 31 July 2008.
This document includes, for each requirement, a corresponding
status, indicating the current situation of the requirement in
XQuery Update
Facility 1.0 at the time that it was issued as a Candidate
Recommendation in March 2008. Three status levels are used:
- "Green" status
-
This indicates that the requirement, according to
its original formulation, has been completely met. Optional
clarificatory text may follow.
- "Yellow" status
-
This indicates that the requirement has been
partially met according to its original formulation. When this
status is indicated, explanatory text is provided to better clarify
the current scope of the requirement.
- "Red" status
-
This indicates that the requirement, according to
its original formulation, has not been met. If this is the case,
explanatory text is provided.
No substantive changes have been made to this specification
since its publication as a Last Call Working Draft.
Please report errors in this document using W3C's public Bugzilla system
(instructions can be found at http://www.w3.org/XML/2005/04/qt-bugzilla).
If access to that system is not feasible, you may send your
comments to the W3C XSLT/XPath/XQuery public comments mailing list,
public-qt-comments@w3.org.
It will be very helpful if you include the string “[UPDreq]” in the
subject line of your report, whether made in Bugzilla or in email.
Each Bugzilla entry and email message should contain only one error
report. Archives of the comments and responses are available at
http://lists.w3.org/Archives/Public/public-qt-comments/.
Publication as a Candidate Recommendation does not imply
endorsement by the W3C Membership. This is a draft document and may
be updated, replaced or obsoleted by other documents at any time.
It is inappropriate to cite this document as other than work in
progress.
This document was produced by a group operating under the
5
February 2004 W3C Patent Policy. W3C maintains a public
list of any patent disclosures made in connection with the
deliverables of the group; that page also includes instructions for
disclosing a patent. An individual who has actual knowledge of a
patent which the individual believes contains
Essential Claim(s) must disclose the information in accordance
with
section 6 of the W3C Patent Policy.
1 Goals
This document describes the requirements for the XQuery Update
Facility. [XQuery 1.0] provides queries, but
has no support for adding new values or changing existing values.
The XML Query Working Group intends to add support for updates in a
future version of XQuery.
2 Usage Scenarios
The following usage scenarios describe how the XQuery Update
Facility may be used in various environments, and represent a wide
range of activities and needs that illustrate the problem space to
be addressed. They are intended to be used as design cases during
the development of the XQuery Update Facility, and should be
reviewed when critical decisions are made. These usage scenarios
should also prove useful in helping non-members of the XML Query
Working Group understand the intent and goals of the project.
- 2.1 Updating persistent XML stores
-
Modify XML in persistent XML stores, including native XML
databases, XML files stored on a file system, or XML stored in SQL
databases.
- 2.2 Modify XML messages
-
Modify XML messages to change status and add information created
while processing the message.
- 2.3 Add to existing XML document
-
Add new data to an existing XML document; for instance, add a
new entry to a BLOG or a data log.
- 2.4 Updating XML registries
-
Perform updates on configuration files, user profiles, or
administrative logs represented in XML.
- 2.5 Creating edited copies
-
Create a new copy of an XML document or subtree that differs
from the original in the way specified by the update. For instance,
updates could be used to modify a web message in order to add new
information and change headers to reflect the modified status.
- 2.6 Modifying XML views
-
Modifying XML views of non-XML sources, such as a [SQL/XML] view of a SQL database.
3 Requirements
3.1 Terminology
The following key words are used throughout the document to
specify the extent to which an item is a requirement for the work
of the XML Query Working Group:
- MUST
-
This word means that the item is an absolute requirement.
- SHOULD
-
This word means that there may exist valid reasons not to treat
this item as a requirement, but the full implications should be
understood and the case carefully weighed before discarding this
item.
- MAY
-
This word means that an item deserves attention, but further
study is needed to determine whether the item should be treated as
a requirement.
When the words MUST, SHOULD, or MAY are used in this technical sense, they
occur as a hyperlink to these definitions. These words will also be
used with their conventional English meaning, in which case there
is no hyperlink. For instance, the phrase "the full implications
should be understood" uses the word "should" in its conventional
English sense, and therefore occurs without the hyperlink.
3.2 General Requirements
- 3.2.1 Query Update Syntax
-
The syntax for updates MAY have
more than one syntax binding. One syntax MUST be convenient for humans to read and
write.
Status: this requirement has been
met.
One syntax MUST be expressed in
XML in a way that reflects the underlying structure of the
operations.
Status: this requirement has been
met.
- 3.2.2 Declarativity
-
The XQuery Update Facility MUST
be declarative. Notably, it MUST be
independent of any particular evaluation strategy.
Status: this requirement has been
met.
- 3.2.3 Protocol Independence
-
The XQuery Update Facility MUST
be defined independently of any protocols with which it is
used.
Status: this requirement has been
met.
- 3.2.4 Error Conditions
-
The XQuery Update Facility MUST
define standard error conditions that can occur during the
execution of an update.
Status: this requirement has been
met.
- 3.2.5 Static Type Checking
-
The XQuery Update Facility SHOULD provide an optional static type
checking feature.
Status: this requirement has been
met.
3.3 Relationship to XQuery
1.0
- 3.3.1 Based on Data Model
-
The XQuery Update Facility MUST
be defined on the [XQuery 1.0 and XPath 2.0
Data Model].
Status: this requirement has been
met.
- 3.3.2 Based on XQuery
-
The XQuery Update Facility MUST
be based on [XQuery 1.0]. The XQuery Update
Facility MUST use XQuery to
identify items to be updated. The XQuery Update Facility MUST use XQuery to specify items used in
the updates.
Status: this requirement has been
met.
3.4 XML Query Update
Functionality
- 3.4.1 Locus of modifications
-
The XQuery Update Facility MUST
be able to change the properties of existing nodes while preserving
their identity. The XQuery Update Facility MUST be able to create a new copy of a node
with a specific set of changes.
Status: this requirement has been
met.
- 3.4.2 Delete
-
The XQuery Update Facility MUST
be able to delete nodes.
Status: this requirement has been
met.
- 3.4.3 Insert
-
The XQuery Update Facility MUST
be able to insert new nodes in specified positions.
Status: this requirement has been
met.
- 3.4.4 Replace
-
The XQuery Update Facility MUST
be able to replace a node.
Status: this requirement has been
met.
- 3.4.5 Changing values
-
The XQuery Update Facility MUST
be able to change the value returned by the typed-value accessor
for a node.
Status: this requirement has been
met.
- 3.4.6 Modifying properties
-
The XQuery Update Facility SHOULD be able to modify some of the
properties of a node such as the name, type, content, nilled,
base-URI, etc.
Status: this requirement has been met.
The base-URI can not be modified.
- 3.4.7 Moving nodes
-
The XQuery Update Facility MAY be
able to move a node from one location to another.
Status: this requirement has not been met.
A node can be deleted, and a copy inserted in a new location, but
it will have a new identity. The Working Group felt that this
functionality would limit the environments in which the XQuery
Update Facility could be implemented.
- 3.4.8 Conditional updates
-
The XQuery Update Facility MUST
be able to do conditional updates.
Status: this requirement has been
met.
- 3.4.9 Iterative updates
-
The XQuery Update Facility MUST
be able to iterate over nodes to do updates.
Status: this requirement has been
met.
- 3.4.10 Validation
-
The XQuery Update Facility MAY
support an explicit XML Schema validation operation that preserves
node identity.
This requirement has not been met according to
its original formulation; however, the revalidation mode can be set
to ensure that type information is recovered and the resulting
document is valid according to the governing schema.
Note:
The XQuery 1.0 validate expression creates a new copy of each
validated node, with a new identity. This requirement involves
preservation of identity.
- 3.4.11 Compositionality
-
The XQuery Update Facility MUST
be able to compose update operators with other update
operators.
Status: this requirement has been
met.
The XQuery Update Facility MAY be
compositional with respect to XQuery expressions; that is, it may
be possible to use an update wherever an XQuery expression is
used.
Status: this requirement has not been met
Updating expressions are limited to specific syntactic
contexts..
- 3.4.12 Parameterization
-
The XQuery Update Facility SHOULD provide a means to parameterize
update operations.
Status: this requirement has been met.
Updating functions and external variables may both be used to
parameterize update operations.
3.5 Transaction
characteristics
In this section, the terms Atomicity, Consistency, Isolation,
and Durability are taken from the ACID model of transaction
characteristics for databases, which is described in [Transaction Processing Concepts and Techniques].
- 3.5.1 Atomicity
-
The XQuery Update Facility MUST
provide a set of atomic operations, and MUST define a means to group atomic
operations into an atomic execution unit.
Status: this requirement has been met.
Multiple atomic operations can be done in a single query, which
constitutes the atomic execution unit.
- 3.5.2 Consistency
-
At the end of an outermost update operation (that is, an update
operation invoked from the external environment), the data model
MUST be consistent with respect to
the constraints specified in the Data Model. In particular, all
type annotations MUST be consistent
with the content of the items they govern.
Status: this requirement has been
met.
The XQuery Update Facility MAY
define additional levels of granularity at which Data Model
constraints are enforced.
Status: this requirement has not been
met.
- 3.5.3 Isolation
-
The XQuery Update Facility SHOULD define the means by which
operations can be isolated from concurrent operations.
The XQuery Update Facility defines operations
purely in terms of the XML Data Model. Propagation of XDM changes
to an underlying persistent store or other software system is
beyond the scope of this specification. This includes
isolation.
- 3.5.4 Durability
-
The XQuery Update Facility MUST
define a means to control the durability of atomic operations and
atomic execution units.
The XQuery Update Facility defines operations
purely in terms of the XML Data Model. Propagation of XDM changes
to an underlying persistent store or other software system is
beyond the scope of this specification. This includes
durability.