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Static Validation of Dynamically Generated XML Documents. A survey on a series of papers by the BRICS research group at the University of Aarhus , Denmark. BRICS = Basic Research in Computer Science www.brics.dk. Dynamic Construction of Web Pages. Interactive Web Services. request.
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Static Validation of Dynamically Generated XML Documents A survey on a series of papers by the BRICS research group at the University of Aarhus, Denmark. BRICS = Basic Research in Computer Science www.brics.dk
Dynamic Construction of Web Pages • Interactive Web Services request response Client with a browser Web server • Application-to-application Web Services Clients are not humans but general programs XML widely used as data interchange format for Web Services Typical solutions: embedded server-side scripting languages (PHP,ASP,JSP,etc) Problems: 1.Linear document construction (printing string fragments to output stream) 2.No compile-time validation of the generated XML (according to a schema)
Approaches to Statically Validate Dynamic XML • Main ideas: 1.Construction based on XML templates (sequences of XML trees • containing named gaps) • 2.Provide compile-time validation of transformed XML documents • An XML schema S describes a set L(S) of XML documents • An XML document X is valid with respect to an XML schema S iff X is in the set L(S) • For a program, verify at compile-time that given that • for each i. • Evolution: • bigwig- high-level C-based domain-specific programming language for developing • interactive Web services; HTML templates are first-class values that may be computed • and stored in variables; • JWIG - Java-based framework for Web service development; a flexible mechanism for • dynamic construction and validation of XML documents, in particular XHTML; • Xact – an extension of JWIG applied on general XML, supports also deconstruction of • XML documents; XML templates are first-class JAVA values;
XML templates An XML template is a well-formed XML fragment with named gaps: <recipe number=[number]> <title><[title]></title> <ingredients><[list]></ingredients> <preparation> <[steps]></preparation> <[nutrition]> </recipe> • There are template gaps and attribute gaps. • Both templates and strings (or arrays of these) can be plugged into template gaps. • Only strings can be plugged into attribute gaps.
ConstructionDeconstructionof XML Templates The plug operation: The select and gapify operations:
Compile-time Output Validation Given an XML transformation T and an XML schema S, is it the case that whenever T outputs an XML document X, then X is valid with respect to S? • This is a hard problem • Practical solution – give approximate but safe (conservative) answers • Perform dataflow analysis using Summary Graphs (a set of XML template values • as nodes, and edges corresponding to possible plugging of gaps) The Program Analyzer • Construct summary graphs for each XML variable at each program point. The • set of summary graphs constitutes a finite lattice (suitable for dataflow analysis). • 2. Construct summary graphs from DTD schemas. • 3. Validate summary graphs (of output XML docs) against DTD schemas. 1. 2. Set of possible XML docs Set of valid XML docs 3.Validation!
Example – no errors import dk.brics.xact.*; public class Hello { XML person = [[ <person><name>John Doe</name></person> ]]; XML html = [[<html> <head><title>Hello</title></head> <body bgcolor="red"> <h1>Hello <[name]></h1> </body> </html> ]]; public XML sayHello() { XML name = person.select("/person/name/text()")[0]; return html.plug("name", name); } public static void main(String[] args) { Hello hello = new Hello(); XML greeting = hello.sayHello(); greeting.analyze("xhtml1-transitional.dtd"); System.out.println(greeting); }} Output Code: <html> <head> <title>Hello</title> </head> <body bgcolor="red"> <h1>Hello John Doe</h1> </body> </html> Browser Output: Hello John Doe
Example – invalid output import dk.brics.xact.*; public class Hello { XML person = [[ <person><name>John Doe</name></person> ]]; XML html = [[<html> <head><title>Hello</title></head> <body gbcolor="red"> <h1>Hello <[name]></h1> </body> </html> ]]; public XML sayHello() { XML name = person.select("/person/name/text()")[0]; return html.plug("name", name); } public static void main(String[] args) { Hello hello = new Hello(); XML greeting = hello.sayHello(); greeting.analyze("xhtml1-transitional.dtd"); System.out.println(greeting); }} Output Code: <html> <head> <title>Hello</title> </head> <body gbcolor="red"> <h1>Hello John Doe</h1> </body> </html> Browser Output: Hello John Doe The XACT analyzer reports the error! *** Invalid XML at line 26 XML template at line 8: attribute gap 'gbcolor' in element 'body' not declared
Example – plug error import dk.brics.xact.*; public class Hello { XML person = [[ <person><name>John Doe</name></person> ]]; XML html = [[<html> <head><title>Hello</title></head> <body bgcolor="red"> <h1>Hello <[name]></h1> </body> </html> ]]; public XML sayHello() { XML name = person.select("/person/name/text()")[0]; return html.plug(“nema", name); } public static void main(String[] args) { Hello hello = new Hello(); XML greeting = hello.sayHello(); greeting.analyze("xhtml1-transitional.dtd"); System.out.println(greeting); }} Output Code: <html> <head> <title>Hello</title> </head> <body bgcolor="red"> <h1>Hello </h1> </body> </html> Browser Output: Hello The XACT analyzer reports the error! *** Inconsistent plug operation at line 20 Template gap 'nema' does not exist
