Chapter 10: XML
اسلاید 1: Chapter 10: XML
اسلاید 2: XMLStructure of XML DataXML Document SchemaQuerying and TransformationApplication Program Interfaces to XMLStorage of XML DataXML Applications
اسلاید 3: IntroductionXML: Extensible Markup LanguageDefined by the WWW Consortium (W3C)Derived from SGML (Standard Generalized Markup Language), but simpler to use than SGML Documents have tags giving extra information about sections of the documentE.g. <title> XML </title> <slide> Introduction …</slide>Extensible, unlike HTMLUsers can add new tags, and separately specify how the tag should be handled for display
اسلاید 4: XML Introduction (Cont.)The ability to specify new tags, and to create nested tag structures make XML a great way to exchange data, not just documents.Much of the use of XML has been in data exchange applications, not as a replacement for HTMLTags make data (relatively) self-documenting E.g. <bank> <account> <account_number> A-101 </account_number> <branch_name> Downtown </branch_name> <balance> 500 </balance> </account> <depositor> <account_number> A-101 </account_number> <customer_name> Johnson </customer_name> </depositor> </bank>
اسلاید 5: XML: MotivationData interchange is critical in today’s networked worldExamples:Banking: funds transferOrder processing (especially inter-company orders)Scientific dataChemistry: ChemML, …Genetics: BSML (Bio-Sequence Markup Language), …Paper flow of information between organizations is being replaced by electronic flow of informationEach application area has its own set of standards for representing informationXML has become the basis for all new generation data interchange formats
اسلاید 6: XML Motivation (Cont.)Earlier generation formats were based on plain text with line headers indicating the meaning of fieldsSimilar in concept to email headersDoes not allow for nested structures, no standard “type” languageTied too closely to low level document structure (lines, spaces, etc)Each XML based standard defines what are valid elements, using XML type specification languages to specify the syntaxDTD (Document Type Descriptors)XML SchemaPlus textual descriptions of the semanticsXML allows new tags to be defined as requiredHowever, this may be constrained by DTDsA wide variety of tools is available for parsing, browsing and querying XML documents/data
اسلاید 7: Comparison with Relational DataInefficient: tags, which in effect represent schema information, are repeatedBetter than relational tuples as a data-exchange formatUnlike relational tuples, XML data is self-documenting due to presence of tagsNon-rigid format: tags can be addedAllows nested structuresWide acceptance, not only in database systems, but also in browsers, tools, and applications
اسلاید 8: Structure of XML DataTag: label for a section of dataElement: section of data beginning with <tagname> and ending with matching </tagname>Elements must be properly nestedProper nesting <account> … <balance> …. </balance> </account> Improper nesting <account> … <balance> …. </account> </balance> Formally: every start tag must have a unique matching end tag, that is in the context of the same parent element.Every document must have a single top-level element
اسلاید 9: Example of Nested Elements <bank-1> <customer> <customer_name> Hayes </customer_name> <customer_street> Main </customer_street> <customer_city> Harrison </customer_city> <account> <account_number> A-102 </account_number> <branch_name> Perryridge </branch_name> <balance> 400 </balance> </account> <account> … </account> </customer> . . </bank-1>
اسلاید 10: Motivation for NestingNesting of data is useful in data transferExample: elements representing customer_id, customer_name, and address nested within an order elementNesting is not supported, or discouraged, in relational databasesWith multiple orders, customer name and address are stored redundantlynormalization replaces nested structures in each order by foreign key into table storing customer name and address informationNesting is supported in object-relational databasesBut nesting is appropriate when transferring dataExternal application does not have direct access to data referenced by a foreign key
اسلاید 11: Structure of XML Data (Cont.)Mixture of text with sub-elements is legal in XML. Example: <account> This account is seldom used any more. <account_number> A-102</account_number> <branch_name> Perryridge</branch_name> <balance>400 </balance> </account>Useful for document markup, but discouraged for data representation
اسلاید 12: AttributesElements can have attributes <account acct-type = “checking” > <account_number> A-102 </account_number> <branch_name> Perryridge </branch_name> <balance> 400 </balance> </account>Attributes are specified by name=value pairs inside the starting tag of an elementAn element may have several attributes, but each attribute name can only occur once<account acct-type = “checking” monthly-fee=“5”>
اسلاید 13: Attributes vs. SubelementsDistinction between subelement and attributeIn the context of documents, attributes are part of markup, while subelement contents are part of the basic document contentsIn the context of data representation, the difference is unclear and may be confusingSame information can be represented in two ways<account account_number = “A-101”> …. </account><account> <account_number>A-101</account_number> … </account>Suggestion: use attributes for identifiers of elements, and use subelements for contents
اسلاید 14: NamespacesXML data has to be exchanged between organizationsSame tag name may have different meaning in different organizations, causing confusion on exchanged documentsSpecifying a unique string as an element name avoids confusionBetter solution: use unique-name:element-nameAvoid using long unique names all over document by using XML Namespaces <bank Xmlns:FB=‘http://www.FirstBank.com’> … <FB:branch> <FB:branchname>Downtown</FB:branchname> <FB:branchcity> Brooklyn </FB:branchcity> </FB:branch> …</bank>
اسلاید 15: More on XML SyntaxElements without subelements or text content can be abbreviated by ending the start tag with a /> and deleting the end tag<account number=“A-101” branch=“Perryridge” balance=“200 />To store string data that may contain tags, without the tags being interpreted as subelements, use CDATA as below<![CDATA[<account> … </account>]]>Here, <account> and </account> are treated as just stringsCDATA stands for “character data”
اسلاید 16: XML Document SchemaDatabase schemas constrain what information can be stored, and the data types of stored valuesXML documents are not required to have an associated schemaHowever, schemas are very important for XML data exchangeOtherwise, a site cannot automatically interpret data received from another siteTwo mechanisms for specifying XML schemaDocument Type Definition (DTD)Widely usedXML Schema Newer, increasing use
اسلاید 17: Document Type Definition (DTD)The type of an XML document can be specified using a DTDDTD constraints structure of XML dataWhat elements can occurWhat attributes can/must an element haveWhat subelements can/must occur inside each element, and how many times.DTD does not constrain data typesAll values represented as strings in XMLDTD syntax<!ELEMENT element (subelements-specification) ><!ATTLIST element (attributes) >
اسلاید 18: Element Specification in DTDSubelements can be specified asnames of elements, or#PCDATA (parsed character data), i.e., character stringsEMPTY (no subelements) or ANY (anything can be a subelement)Example<! ELEMENT depositor (customer_name account_number)> <! ELEMENT customer_name (#PCDATA)><! ELEMENT account_number (#PCDATA)>Subelement specification may have regular expressions <!ELEMENT bank ( ( account | customer | depositor)+)>Notation: “|” - alternatives “+” - 1 or more occurrences “*” - 0 or more occurrences
اسلاید 19: Bank DTD<!DOCTYPE bank [<!ELEMENT bank ( ( account | customer | depositor)+)><!ELEMENT account (account_number branch_name balance)><! ELEMENT customer(customer_name customer_street customer_city)><! ELEMENT depositor (customer_name account_number)><! ELEMENT account_number (#PCDATA)><! ELEMENT branch_name (#PCDATA)><! ELEMENT balance(#PCDATA)><! ELEMENT customer_name(#PCDATA)><! ELEMENT customer_street(#PCDATA)><! ELEMENT customer_city(#PCDATA)>]>
اسلاید 20: Attribute Specification in DTDAttribute specification : for each attribute NameType of attribute CDATAID (identifier) or IDREF (ID reference) or IDREFS (multiple IDREFs) more on this later Whether mandatory (#REQUIRED)has a default value (value), or neither (#IMPLIED)Examples<!ATTLIST account acct-type CDATA “checking”><!ATTLIST customercustomer_id ID # REQUIREDaccounts IDREFS # REQUIRED >
اسلاید 21: IDs and IDREFsAn element can have at most one attribute of type IDThe ID attribute value of each element in an XML document must be distinctThus the ID attribute value is an object identifierAn attribute of type IDREF must contain the ID value of an element in the same documentAn attribute of type IDREFS contains a set of (0 or more) ID values. Each ID value must contain the ID value of an element in the same document
اسلاید 22: Bank DTD with AttributesBank DTD with ID and IDREF attribute types. <!DOCTYPE bank-2[ <!ELEMENT account (branch, balance)> <!ATTLIST account account_number ID # REQUIRED owners IDREFS # REQUIRED> <!ELEMENT customer(customer_name, customer_street, customer_city)> <!ATTLIST customer customer_id ID # REQUIRED accounts IDREFS # REQUIRED> … declarations for branch, balance, customer_name, customer_street and customer_city ]>
اسلاید 23: XML data with ID and IDREF attributes<bank-2><account account_number=“A-401” owners=“C100 C102”> <branch_name> Downtown </branch_name> <balance> 500 </balance></account><customer customer_id=“C100” accounts=“A-401”> <customer_name>Joe </customer_name> <customer_street> Monroe </customer_street> <customer_city> Madison</customer_city></customer><customer customer_id=“C102” accounts=“A-401 A-402”> <customer_name> Mary </customer_name> <customer_street> Erin </customer_street> <customer_city> Newark </customer_city></customer></bank-2>
اسلاید 24: Limitations of DTDsNo typing of text elements and attributesAll values are strings, no integers, reals, etc.Difficult to specify unordered sets of subelementsOrder is usually irrelevant in databases (unlike in the document-layout environment from which XML evolved)(A | B)* allows specification of an unordered set, butCannot ensure that each of A and B occurs only onceIDs and IDREFs are untypedThe owners attribute of an account may contain a reference to another account, which is meaninglessowners attribute should ideally be constrained to refer to customer elements
اسلاید 25: XML SchemaXML Schema is a more sophisticated schema language which addresses the drawbacks of DTDs. SupportsTyping of valuesE.g. integer, string, etcAlso, constraints on min/max valuesUser-defined, comlex typesMany more features, includinguniqueness and foreign key constraints, inheritance XML Schema is itself specified in XML syntax, unlike DTDsMore-standard representation, but verboseXML Scheme is integrated with namespaces BUT: XML Schema is significantly more complicated than DTDs.
اسلاید 26: XML Schema Version of Bank DTD<xs:schema xmlns:xs=http://www.w3.org/2001/XMLSchema><xs:element name=“bank” type=“BankType”/><xs:element name=“account”> <xs:complexType> <xs:sequence> <xs:element name=“account_number” type=“xs:string”/> <xs:element name=“branch_name” type=“xs:string”/> <xs:element name=“balance” type=“xs:decimal”/> </xs:squence> </xs:complexType></xs:element>….. definitions of customer and depositor ….<xs:complexType name=“BankType”> <xs:squence><xs:element ref=“account” minOccurs=“0” maxOccurs=“unbounded”/><xs:element ref=“customer” minOccurs=“0” maxOccurs=“unbounded”/><xs:element ref=“depositor” minOccurs=“0” maxOccurs=“unbounded”/></xs:sequence></xs:complexType></xs:schema>
اسلاید 27: XML Schema Version of Bank DTDChoice of “xs:” was ours -- any other namespace prefix could be chosenElement “bank” has type “BankType”, which is defined separatelyxs:complexType is used later to create the named complex type “BankType”Element “account” has its type defined in-line
اسلاید 28: More features of XML SchemaAttributes specified by xs:attribute tag:<xs:attribute name = “account_number”/>adding the attribute use = “required” means value must be specifiedKey constraint: “account numbers form a key for account elements under the root bank element:<xs:key name = “accountKey”><xs:selector xpath = “]bank/account”/><xs:field xpath = “account_number”/><xs:key>Foreign key constraint from depositor to account:<xs:keyref name = “depositorAccountKey” refer=“accountKey”><xs:selector xpath = “]bank/account”/><xs:field xpath = “account_number”/><xs:keyref>
اسلاید 29: Querying and Transforming XML DataTranslation of information from one XML schema to anotherQuerying on XML data Above two are closely related, and handled by the same toolsStandard XML querying/translation languagesXPathSimple language consisting of path expressionsXSLTSimple language designed for translation from XML to XML and XML to HTMLXQueryAn XML query language with a rich set of features
اسلاید 30: Tree Model of XML DataQuery and transformation languages are based on a tree model of XML dataAn XML document is modeled as a tree, with nodes corresponding to elements and attributesElement nodes have child nodes, which can be attributes or subelementsText in an element is modeled as a text node child of the elementChildren of a node are ordered according to their order in the XML documentElement and attribute nodes (except for the root node) have a single parent, which is an element nodeThe root node has a single child, which is the root element of the document
اسلاید 31: XPathXPath is used to address (select) parts of documents using path expressionsA path expression is a sequence of steps separated by “/”Think of file names in a directory hierarchyResult of path expression: set of values that along with their containing elements/attributes match the specified path E.g. /bank-2/customer/customer_name evaluated on the bank-2 data we saw earlier returns <customer_name>Joe</customer_name><customer_name>Mary</customer_name>E.g. /bank-2/customer/customer_name/text( ) returns the same names, but without the enclosing tags
اسلاید 32: XPath (Cont.)The initial “/” denotes root of the document (above the top-level tag)Path expressions are evaluated left to rightEach step operates on the set of instances produced by the previous stepSelection predicates may follow any step in a path, in [ ]E.g. /bank-2/account[balance > 400] returns account elements with a balance value greater than 400/bank-2/account[balance] returns account elements containing a balance subelementAttributes are accessed using “@”E.g. /bank-2/account[balance > 400]/@account_numberreturns the account numbers of accounts with balance > 400IDREF attributes are not dereferenced automatically (more on this later)
اسلاید 33: Functions in XPathXPath provides several functionsThe function count() at the end of a path counts the number of elements in the set generated by the pathE.g. /bank-2/account[count(./customer) > 2] Returns accounts with > 2 customersAlso function for testing position (1, 2, ..) of node w.r.t. siblingsBoolean connectives and and or and function not() can be used in predicatesIDREFs can be referenced using function id()id() can also be applied to sets of references such as IDREFS and even to strings containing multiple references separated by blanksE.g. /bank-2/account/id(@owner) returns all customers referred to from the owners attribute of account elements.
اسلاید 34: More XPath FeaturesOperator “|” used to implement union E.g. /bank-2/account/id(@owner) | /bank-2/loan/id(@borrower)Gives customers with either accounts or loansHowever, “|” cannot be nested inside other operators.“//” can be used to skip multiple levels of nodes E.g. /bank-2//customer_name finds any customer_name element anywhere under the /bank-2 element, regardless of the element in which it is contained.A step in the path can go to parents, siblings, ancestors and descendants of the nodes generated by the previous step, not just to the children“//”, described above, is a short from for specifying “all descendants”“..” specifies the parent.doc(name) returns the root of a named document
اسلاید 35: XQueryXQuery is a general purpose query language for XML data Currently being standardized by the World Wide Web Consortium (W3C)The textbook description is based on a January 2005 draft of the standard. The final version may differ, but major features likely to stay unchanged.XQuery is derived from the Quilt query language, which itself borrows from SQL, XQL and XML-QLXQuery uses a for … let … where … order by …result … syntax for SQL from where SQL where order by SQL order by result SQL select let allows temporary variables, and has no equivalent in SQL
اسلاید 36: FLWOR Syntax in XQuery For clause uses XPath expressions, and variable in for clause ranges over values in the set returned by XPathSimple FLWOR expression in XQuery find all accounts with balance > 400, with each result enclosed in an <account_number> .. </account_number> tag for $x in /bank-2/account let $acctno := $x/@account_number where $x/balance > 400 return <account_number> { $acctno } </account_number>Items in the return clause are XML text unless enclosed in {}, in which case they are evaluatedLet clause not really needed in this query, and selection can be done In XPath. Query can be written as:for $x in /bank-2/account[balance>400] return <account_number> { $x/@account_number } </account_number>
اسلاید 37: JoinsJoins are specified in a manner very similar to SQL for $a in /bank/account, $c in /bank/customer, $d in /bank/depositor where $a/account_number = $d/account_number and $c/customer_name = $d/customer_name return <cust_acct> { $c $a } </cust_acct>The same query can be expressed with the selections specified as XPath selections: for $a in /bank/account $c in /bank/customer $d in /bank/depositor[ account_number = $a/account_number and customer_name = $c/customer_name] return <cust_acct> { $c $a } </cust_acct>
اسلاید 38: Nested QueriesThe following query converts data from the flat structure for bank information into the nested structure used in bank-1 <bank-1> { for $c in /bank/customer return <customer> { $c/* } { for $d in /bank/depositor[customer_name = $c/customer_name], $a in /bank/account[account_number=$d/account_number] return $a } </customer> } </bank-1>$c/* denotes all the children of the node to which $c is bound, without the enclosing top-level tag$c/text() gives text content of an element without any subelements / tags
اسلاید 39: Sorting in XQuery The order by clause can be used at the end of any expression. E.g. to return customers sorted by name for $c in /bank/customer order by $c/customer_name return <customer> { $c/* } </customer>Use order by $c/customer_name to sort in descending orderCan sort at multiple levels of nesting (sort by customer_name, and by account_number within each customer) <bank-1> { for $c in /bank/customer order by $c/customer_namereturn <customer> { $c/* } { for $d in /bank/depositor[customer_name=$c/customer_name], $a in /bank/account[account_number=$d/account_number] }order by $a/account_number return <account> $a/* </account> </customer> } </bank-1>
اسلاید 40: Functions and Other XQuery FeaturesUser defined functions with the type system of XMLSchema function balances(xs:string $c) returns list(xs:decimal*) { for $d in /bank/depositor[customer_name = $c], $a in /bank/account[account_number = $d/account_number] return $a/balance }Types are optional for function parameters and return valuesThe * (as in decimal*) indicates a sequence of values of that typeUniversal and existential quantification in where clause predicatessome $e in path satisfies P every $e in path satisfies P XQuery also supports If-then-else clauses
اسلاید 41: XSLTA stylesheet stores formatting options for a document, usually separately from documentE.g. an HTML style sheet may specify font colors and sizes for headings, etc.The XML Stylesheet Language (XSL) was originally designed for generating HTML from XMLXSLT is a general-purpose transformation language Can translate XML to XML, and XML to HTMLXSLT transformations are expressed using rules called templatesTemplates combine selection using XPath with construction of results
اسلاید 42: XSLT TemplatesExample of XSLT template with match and select part <xsl:template match=“/bank-2/customer”> <xsl:value-of select=“customer_name”/> </xsl:template> <xsl:template match=“*”/>The match attribute of xsl:template specifies a pattern in XPathElements in the XML document matching the pattern are processed by the actions within the xsl:template elementxsl:value-of selects (outputs) specified values (here, customer_name)For elements that do not match any template Attributes and text contents are output as isTemplates are recursively applied on subelementsThe <xsl:template match=“*”/> template matches all elements that do not match any other templateUsed to ensure that their contents do not get output.If an element matches several templates, only one is used based on a complex priority scheme/user-defined priorities
اسلاید 43: Creating XML OutputAny text or tag in the XSL stylesheet that is not in the xsl namespace is output as isE.g. to wrap results in new XML elements. <xsl:template match=“/bank-2/customer”> <customer> <xsl:value-of select=“customer_name”/> </customer> </xsl;template> <xsl:template match=“*”/>Example output: <customer> Joe </customer> <customer> Mary </customer>
اسلاید 44: Creating XML Output (Cont.)Note: Cannot directly insert a xsl:value-of tag inside another tagE.g. cannot create an attribute for <customer> in the previous example by directly using xsl:value-ofXSLT provides a construct xsl:attribute to handle this situationxsl:attribute adds attribute to the preceding elementE.g. <customer> <xsl:attribute name=“customer_id”> <xsl:value-of select = “customer_id”/> </xsl:attribute> </customer> results in output of the form <customer customer_id=“….”> ….xsl:element is used to create output elements with computed names
اسلاید 45: Structural RecursionTemplate action can apply templates recursively to the contents of a matched element <xsl:template match=“/bank”> <customers> <xsl:template apply-templates/> </customers > </xsl:template> <xsl:template match=“/customer”> <customer> <xsl:value-of select=“customer_name”/> </customer> </xsl:template> <xsl:template match=“*”/>Example output: <customers> <customer> John </customer> <customer> Mary </customer> </customers>
اسلاید 46: Joins in XSLTXSLT keys allow elements to be looked up (indexed) by values of subelements or attributesKeys must be declared (with a name) and, the key() function can then be used for lookup. E.g. <xsl:key name=“acctno” match=“account” use=“account_number”/><xsl:value-of select=key(“acctno”, “A-101”)Keys permit (some) joins to be expressed in XSLT<xsl:key name=“acctno” match=“account” use=“account_number”/><xsl:key name=“custno” match=“customer” use=“customer_name”/><xsl:template match=“depositor”><cust_acct><xsl:value-of select=key(“custno”, “customer_name”)/><xsl:value-of select=key(“acctno”, “account_number”)/></cust_acct></xsl:template><xsl:template match=“*”/>
اسلاید 47: Sorting in XSLTUsing an xsl:sort directive inside a template causes all elements matching the template to be sorted Sorting is done before applying other templates<xsl:template match=“/bank”> <xsl:apply-templates select=“customer”> <xsl:sort select=“customer_name”/> </xsl:apply-templates> </xsl:template> <xsl:template match=“customer”> <customer> <xsl:value-of select=“customer_name”/> <xsl:value-of select=“customer_street”/> <xsl:value-of select=“customer_city”/> </customer> <xsl:template> <xsl:template match=“*”/>
اسلاید 48: Application Program InterfaceThere are two standard application program interfaces to XML data:SAX (Simple API for XML)Based on parser model, user provides event handlers for parsing events E.g. start of element, end of elementNot suitable for database applicationsDOM (Document Object Model)XML data is parsed into a tree representation Variety of functions provided for traversing the DOM treeE.g.: Java DOM API provides Node class with methods getParentNode( ), getFirstChild( ), getNextSibling( ) getAttribute( ), getData( ) (for text node) getElementsByTagName( ), …Also provides functions for updating DOM tree
اسلاید 49: Storage of XML DataXML data can be stored in Non-relational data storesFlat filesNatural for storing XMLBut has all problems discussed in Chapter 1 (no concurrency, no recovery, …)XML databaseDatabase built specifically for storing XML data, supporting DOM model and declarative queryingCurrently no commercial-grade systemsRelational databasesData must be translated into relational formAdvantage: mature database systemsDisadvantages: overhead of translating data and queries
اسلاید 50: Storage of XML in Relational DatabasesAlternatives:String RepresentationTree RepresentationMap to relations
اسلاید 51: String RepresentationStore each top level element as a string field of a tuple in a relational databaseUse a single relation to store all elements, orUse a separate relation for each top-level element typeE.g. account, customer, depositor relationsEach with a string-valued attribute to store the elementIndexing:Store values of subelements/attributes to be indexed as extra fields of the relation, and build indices on these fieldsE.g. customer_name or account_numberSome database systems support function indices, which use the result of a function as the key value. The function should return the value of the required subelement/attribute
اسلاید 52: String Representation (Cont.)Benefits: Can store any XML data even without DTDAs long as there are many top-level elements in a document, strings are small compared to full documentAllows fast access to individual elements.Drawback: Need to parse strings to access values inside the elementsParsing is slow.
اسلاید 53: Tree RepresentationTree representation: model XML data as tree and store using relations nodes(id, type, label, value) child (child_id, parent_id) Each element/attribute is given a unique identifierType indicates element/attributeLabel specifies the tag name of the element/name of attributeValue is the text value of the element/attributeThe relation child notes the parent-child relationships in the treeCan add an extra attribute to child to record ordering of childrenbank (id:1)customer (id:2)account (id: 5)customer_name (id: 3)account_number (id: 7)
اسلاید 54: Tree Representation (Cont.)Benefit: Can store any XML data, even without DTDDrawbacks:Data is broken up into too many pieces, increasing space overheadsEven simple queries require a large number of joins, which can be slow
اسلاید 55: Mapping XML Data to RelationsRelation created for each element type whose schema is known:An id attribute to store a unique id for each elementA relation attribute corresponding to each element attributeA parent_id attribute to keep track of parent elementAs in the tree representationPosition information (ith child) can be store tooAll subelements that occur only once can become relation attributesFor text-valued subelements, store the text as attribute valueFor complex subelements, can store the id of the subelementSubelements that can occur multiple times represented in a separate tableSimilar to handling of multivalued attributes when converting ER diagrams to tables
اسلاید 56: Storing XML Data in Relational SystemsPublishing: process of converting relational data to an XML formatShredding: process of converting an XML document into a set of tuples to be inserted into one or more relationsXML-enabled database systems support automated publishing and shreddingSome systems offer native storage of XML data using the xml data type. Special internal data structures and indices are used for efficiency
اسلاید 57: SQL/XMLNew standard SQL extension that allows creation of nested XML outputEach output tuple is mapped to an XML element row<bank><account><row><account_number> A-101 </account_number><branch_name> Downtown </branch_name><balance> 500 </balance></row>…. more rows if there are more output tuples …</account></bank>
اسلاید 58: SQL Extensionsxmlelement creates XML elementsxmlattributes creates attributesselect xmlelement (name “account,xmlattributes (account_number as account_number),xmlelement (name “branch_name”, branch_name),xmlelement (name “balance”, balance))from account
اسلاید 59: Web ServicesThe Simple Object Access Protocol (SOAP) standard:Invocation of procedures across applications with distinct databasesXML used to represent procedure input and outputA Web service is a site providing a collection of SOAP proceduresDescribed using the Web Services Description Language (WSDL)Directories of Web services are described using the Universal Description, Discovery, and Integration (UDDI) standard
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