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47-471: Use of the standardized USMTF allows ATO processing by a variety of legacy computer models, newer software, and even word processors. Since 2004, the ATO has been standardized as an XML schema by NATO Allied Data Publication-3 and US MIL-STD-6040. The ATO was historically known as the "fragmentary order" or "frag order" or “Frag-O” or "FRAGO". Pilots continue to informally refer to it as the "frag"; to be "fragged" to

94-486: A RELAX NG schema across multiple validators requires either providing those user-defined data types to that validator or using only the two basic types. In practice, however, most RELAX NG processors support the W3C XML Schema set of data types. Schematron is a fairly unusual schema language. Unlike the main three, it defines an XML file's syntax as a list of XPath -based rules. If the document passes these rules, then it

141-423: A collection of schema documents , which contain the source language definitions of these components. In popular usage, however, a schema document is often referred to as a schema. Schema documents are organized by namespace: all the named schema components belong to a target namespace, and the target namespace is a property of the schema document as a whole. A schema document may include other schema documents for

188-508: A complex type may be constrained by assertions— XPath 2.0 expressions evaluated against the content that must evaluate to true. After XML Schema-based validation, it is possible to express an XML document's structure and content in terms of the data model that was implicit during validation. The XML Schema data model includes: This collection of information is called the Post-Schema-Validation Infoset (PSVI). The PSVI gives

235-411: A degree of modularity in their languages, including, for example, splitting the schema into multiple files. And both of them are, or can be, defined in an XML language. RELAX NG does not have any analog to PSVI . Unlike W3C XML Schema, RELAX NG was designed so that validation and augmentation (adding type information and default values) are separate. W3C XML Schema has a formal mechanism for attaching

282-588: A mission is to be assigned to it, and "as fragged" indicates that an operation will/did occur in accordance with the original ATO, without modifications. As defined by Joint Publication 1-02, an air tasking order is: "A method used to task and disseminate to components, subordinate units, and command and control agencies projected sorties, capabilities, and/or forces to targets and specific missions. Normally provides specific instructions to include call signs, targets, controlling agencies, etc., as well as general instructions." This United States Air Force article

329-595: A particular element, and so forth. A schema is analogous to a grammar for a language; a schema defines what the vocabulary for the language may be and what a valid "sentence" is. There are historic and current XML schema languages: The main ones (see also the ISO 19757's endorsed languages ) are described below. Though there are a number of schema languages available, the primary three languages are Document Type Definitions , W3C XML Schema , and RELAX NG . Each language has its own advantages and disadvantages. DTDs are perhaps

376-524: A potential security problem. For WXS validators that will follow a URI to an arbitrary online location, there is the potential for reading something malicious from the other side of the stream. W3C XML Schema does not implement most of the DTD ability to provide data elements to a document. Although W3C XML Schema's ability to add default attributes to elements is an advantage, it is a disadvantage in some ways as well. It means that an XML file may not be usable in

423-595: A recommendation of the World Wide Web Consortium ( W3C ), specifies how to formally describe the elements in an Extensible Markup Language ( XML ) document. It can be used by programmers to verify each piece of item content in a document, to assure it adheres to the description of the element it is placed in. Like all XML schema languages , XSD can be used to express a set of rules to which an XML document must conform to be considered "valid" according to that schema. However, unlike most other schema languages, XSD

470-429: A schema are: Other more specialized components include annotations, assertions, notations, and the schema component which contains information about the schema as a whole. Simple types (also called data types) constrain the textual values that may appear in an element or attribute. This is one of the more significant ways in which XML Schema differs from DTDs. For example, an attribute might be constrained to hold only

517-502: A schema can be regarded as a conceptually separate operation from XML parsing. In practice, however, many schema validators are integrated with an XML parser. There are several different languages available for specifying an XML schema. Each language has its strengths and weaknesses. The primary purpose of a schema language is to specify what the structure of an XML document can be. This means which elements can reside in which other elements, which attributes are and are not legal to have on

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564-584: A schema to an XML document, while RELAX NG intentionally avoids such mechanisms for security and interoperability reasons. RELAX NG has no ability to apply default attribute data to an element's list of attributes (i.e., changing the XML info set), while W3C XML Schema does. Again, this design is intentional and is to separate validation and augmentation. W3C XML Schema has a rich "simple type" system built-in (xs:number, xs:date, etc., plus derivation of custom types), while RELAX NG has an extremely simplistic one because it

611-468: A valid XML document its "type" and facilitates treating the document as an object, using object-oriented programming (OOP) paradigms. The primary reason for defining an XML schema is to formally describe an XML document; however the resulting schema has a number of other uses that go beyond simple validation. The schema can be used to generate code, referred to as XML Data Binding . This code allows contents of XML documents to be treated as objects within

658-465: A valid date or a decimal number. XSD provides a set of 19 primitive data types ( anyURI , base64Binary , boolean , date , dateTime , decimal , double , duration , float , hexBinary , gDay , gMonth , gMonthDay , gYear , gYearMonth , NOTATION , QName , string , and time ). It allows new data types to be constructed from these primitives by three mechanisms: Twenty-five derived types are defined within

705-408: Is a stub . You can help Misplaced Pages by expanding it . XML schema An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself. These constraints are generally expressed using some combination of grammatical rules governing

752-466: Is actually an XSLT transformation that transforms the Schematron document into an XSLT that validates the XML file. As such, Schematron's potential toolset is any XSLT processor, though libxml2 provides an implementation that does not require XSLT. Sun Microsystems 's Multiple Schema Validator for Java has an add-on that allows it to validate RELAX NG schemas that have embedded Schematron rules. This

799-550: Is commonly referred to as XSD. The process of checking to see if a XML document conforms to a schema is called validation , which is separate from XML's core concept of syntactic well-formedness . All XML documents must be well-formed, but it is not required that a document be valid unless the XML parser is "validating", in which case the document is also checked for conformance with its associated schema. DTD-validating parsers are most common, but some support XML Schema or RELAX NG as well. Validation of an instance document against

846-416: Is complex and hard to learn, although that is partially because it tries to do more than mere validation (see PSVI ). Although being written in XML is an advantage, it is also a disadvantage in some ways. The W3C XML Schema language, in particular, can be quite verbose, while a DTD can be terse and relatively easily editable. Likewise, WXS's formal mechanism for associating a document with a schema can pose

893-453: Is designed to make manipulation of the XML instance easier in application programs. This may be by mapping the XSD-defined types to types in a programming language such as Java ("data binding") or by enriching the type system of XML processing languages such as XSLT and XQuery (known as "schema-awareness"). RELAX NG and W3C XML Schema allow for similar mechanisms of specificity. Both allow for

940-458: Is known as the compact syntax. Tools can easily convert between these forms with no loss of features or even commenting. Even arbitrary elements specified between RELAX NG XML elements can be converted into the compact form. RELAX NG provides very strong support for unordered content. That is, it allows the schema to state that a sequence of patterns may appear in any order. RELAX NG also allows for non-deterministic content models. What this means

987-553: Is meant to use type libraries developed independently of RELAX NG, rather than grow its own. This is seen by some as a disadvantage. In practice it is common for a RELAX NG schema to use the predefined "simple types" and "restrictions" (pattern, maxLength, etc.) of W3C XML Schema. In W3C XML Schema a specific number or range of repetitions of patterns can be expressed whereas it is practically not possible to specify at all in RELAX NG (<oneOrMore> or <zeroOrMore>). W3C XML Schema

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1034-459: Is not technically a schema language. Its sole purpose is to direct parts of documents to individual schemas based on the namespace of the encountered elements. An NRL is merely a list of XML namespaces and a path to a schema that each corresponds to. This allows each schema to be concerned with only its own language definition, and the NRL file routes the schema validator to the correct schema file based on

1081-457: Is of relatively limited capability, but that also has other uses in XML aside from the expression of schemas. Two more expressive XML schema languages in widespread use are XML Schema (with a capital S ) and RELAX NG . The mechanism for associating an XML document with a schema varies according to the schema language. The association may be achieved via markup within the XML document itself, or via some external means. The XML Schema Definition

1128-441: Is successful in that it has been widely adopted and largely achieves what it set out to, it has been the subject of a great deal of severe criticism, perhaps more so than any other W3C Recommendation. Good summaries of the criticisms are provided by James Clark, Anders Møller and Michael Schwartzbach, Rick Jelliffe and David Webber. General problems: Practical limitations of expressibility: Technical problems: XSD 1.1 became

1175-424: Is that RELAX NG allows the specification of a sequence like the following: When the validator encounters something that matches the "odd" pattern, it is unknown whether this is the optional last "odd" reference or simply one in the zeroOrMore sequence without looking ahead at the data. RELAX NG allows this kind of specification. W3C XML Schema requires all of its sequences to be fully deterministic, so mechanisms like

1222-504: Is the name used in this article. In its appendix of references, the XSD specification acknowledges the influence of DTDs and other early XML schema efforts such as DDML , SOX , XML-Data, and XDR . It has adopted features from each of these proposals but is also a compromise among them. Of those languages, XDR and SOX continued to be used and supported for a while after XML Schema was published. A number of Microsoft products supported XDR until

1269-444: Is valid. Because of its rule-based nature, Schematron's specificity is very strong. It can require that the content of an element be controlled by one of its siblings. It can also request or require that the root element, regardless of what element that happens to be, have specific attributes. It can even specify required relationships between multiple XML files. While Schematron is good at relational constructs, its ability to specify

1316-460: The W3C. Because of confusion between XML Schema as a specific W3C specification, and the use of the same term to describe schema languages in general, some parts of the user community referred to this language as WXS , an initialism for W3C XML Schema, while others referred to it as XSD , an initialism for XML Schema Definition. In Version 1.1 the W3C has chosen to adopt XSD as the preferred name, and that

1363-405: The above must be either specified in a different way or omitted altogether. RELAX NG allows attributes to be treated as elements in content models. In particular, this means that one can provide the following: This block states that the element "some_element" must have an attribute named "has_name". This attribute can only take true or false as values, and if it is true, the first child element of

1410-424: The absence of its schema, even if the document would validate against that schema. In effect, all users of such an XML document must also implement the W3C XML Schema specification, thus ruling out minimalist or older XML parsers. It can also slow down the processing of the document, as the processor must potentially download and process a second XML file (the schema); however, a schema would normally then be cached, so

1457-453: The basic structure of a document, that is, which elements can go where, results in a very verbose schema. The typical way to solve this is to combine Schematron with RELAX NG or W3C XML Schema. There are several schema processors available for both languages that support this combined form. This allows Schematron rules to specify additional constraints to the structure defined by W3C XML Schema or RELAX NG. Schematron's reference implementation

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1504-450: The client invoking validation to trust the document sufficiently to know that it is being validated against the correct schema. "xsi" is the conventional prefix for the namespace " http://www.w3.org/2001/XMLSchema-instance ".) XML Schema Documents usually have the filename extension ".xsd". A unique Internet Media Type is not yet registered for XSDs, so "application/xml" or "text/xml" should be used, as per RFC 3023. The main components of

1551-444: The cost comes only on the first use. WXS support exists in a number of large XML parsing packages. Xerces and the .NET Framework 's Base Class Library both provide support for WXS validation. RELAX NG provides for most of the advantages that W3C XML Schema does over DTDs. While the language of RELAX NG can be written in XML, it also has an equivalent form that is much more like a DTD, but with greater specifying power. This form

1598-402: The definition of many more. In theory, the lack of a specific list allows a processor to support data types that are very problem-domain specific. Most RELAX NG schemas can be algorithmically converted into W3C XML Schemas and even DTDs (except when using RELAX NG features not supported by those languages, as above). The reverse is not true. As such, RELAX NG can be used as a normative version of

1645-524: The element must be "name", which stores text. If "name" did not need to be the first element, then the choice could be wrapped in an "interleave" element along with other elements. The order of the specification of attributes in RELAX NG has no meaning, so this block need not be the first block in the element definition. W3C XML Schema cannot specify such a dependency between the content of an attribute and child elements. RELAX NG's specification only lists two built-in types (string and token), but it allows for

1692-800: The most widely supported schema language for XML. Because DTDs are one of the earliest schema languages for XML, defined before XML even had namespace support, they are widely supported. Internal DTDs are often supported in XML processors; external DTDs are less often supported, but only slightly. Most large XML parsers, ones that support multiple XML technologies, will provide support for DTDs as well. Features available in XSD that are missing from DTDs include: XSD schemas are conventionally written as XML documents, so familiar editing and transformation tools can be used. As well as validation, XSD allows XML instances to be annotated with type information (the Post-Schema-Validation Infoset (PSVI) ) which

1739-479: The namespace of that element. This XML format is schema-language agnostic and works for just about any schema language. Capitalization in the schema word: there is some confusion as to when to use the capitalized spelling "Schema" and when to use the lowercase spelling. The lowercase form is a generic term and may refer to any type of schema, including DTD, XML Schema (aka XSD), RELAX NG, or others, and should always be written using lowercase except when appearing at

1786-408: The order of elements, Boolean predicates that the content must satisfy, data types governing the content of elements and attributes, and more specialized rules such as uniqueness and referential integrity constraints. There are languages developed specifically to express XML schemas. The document type definition (DTD) language, which is native to the XML specification, is a schema language that

1833-451: The permitted content of an element, including its element and text children and its attributes. A complex type definition consists of a set of attribute uses and a content model. Varieties of content model include: A complex type can be derived from another complex type by restriction (disallowing some elements, attributes, or values that the base type permits) or by extension (allowing additional attributes and elements to appear). In XSD 1.1,

1880-465: The programming environment. The schema can be used to generate human-readable documentation of an XML file structure; this is especially useful where the authors have made use of the annotation elements. No formal standard exists for documentation generation, but a number of tools are available, such as the Xs3p stylesheet, that will produce high-quality readable HTML and printed material. Although XML Schema

1927-558: The release of MSXML 6.0 (which dropped XDR in favor of XML Schema) in December 2006. Commerce One , Inc. supported its SOX schema language until declaring bankruptcy in late 2004. The most obvious features offered in XSD that are not available in XML's native Document Type Definitions (DTDs) are namespace awareness and datatypes, that is, the ability to define element and attribute content as containing values such as integers and dates rather than arbitrary text. The XSD 1.0 specification

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1974-457: The same namespace, and may import schema documents for a different namespace. When an instance document is validated against a schema (a process known as assessment ), the schema to be used for validation can either be supplied as a parameter to the validation engine, or it can be referenced directly from the instance document using two special attributes, xsi:schemaLocation and xsi:noNamespaceSchemaLocation . (The latter mechanism requires

2021-402: The schema, and the user can convert it to other forms for tools that do not support RELAX NG. Most of RELAX NG's disadvantages are covered under the section on W3C XML Schema's advantages over RELAX NG. Though RELAX NG's ability to support user-defined data types is useful, it comes at the disadvantage of only having two data types that the user can rely upon. Which, in theory, means that using

2068-470: The specification itself, and further derived types can be defined by users in their own schemas. The mechanisms available for restricting data types include the ability to specify minimum and maximum values, regular expressions, constraints on the length of strings, and constraints on the number of digits in decimal values. XSD 1.1 again adds assertions, the ability to specify an arbitrary constraint by means of an XPath 2.0 expression. Complex types describe

2115-649: The start of a sentence. The form "Schema" (capitalized) in common use in the XML community always refers to W3C XML Schema . The focus of the schema definition is structure and some semantics of documents. However, schema design, just like design of databases, computer program, and other formal constructs, also involve many considerations of style, convention, and readability. Extensive discussions of schema design issues can be found in (for example) Maler (1995) and DeRose (1997). Languages: PSVI 1.0, Part 2 Datatypes (Recommendation) , 1.1, Part 1 Structures (Recommendation) , XSD ( XML Schema Definition ),

2162-502: Was also designed with the intent that determination of a document's validity would produce a collection of information adhering to specific data types . Such a post-validation infoset can be useful in the development of XML document processing software. XML Schema , published as a W3C recommendation in May 2001, is one of several XML schema languages . It was the first separate schema language for XML to achieve Recommendation status by

2209-455: Was originally published in 2001, with a second edition following in 2004 to correct large numbers of errors. XSD 1.1 became a W3C Recommendation in April 2012 . Technically, a schema is an abstract collection of metadata, consisting of a set of schema components : chiefly element and attribute declarations and complex and simple type definitions. These components are usually created by processing

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