A Rule Based System For Web Site Verification D. Ballis 1 J. García-Vivó 2 1 Dip. Matematica e Informatica, Via delle Scienze 206, Udine, Italy DSIC, Universidad Politécnica de Valencia, Camino de Vera s/n, Apdo , Valencia, Spain.

Motivations Web Sites can have a very complex structure Web Sites can have a very complex structure Development and maintenance of Web sites are difficult tasks Development and maintenance of Web sites are difficult tasks Suitable methodologies are needed to verify Web sites w.r.t. syntactic as well as semantic properties! Suitable methodologies are needed to verify Web sites w.r.t. syntactic as well as semantic properties!

Formal Verification of Web Sites GVerdi, the graphical evolution of the VERDI system, implements: GVerdi, the graphical evolution of the VERDI system, implements: – a rule-based specification language for specifying properties of Web sites – a verification technique for automatically checking whether the conditions are fulfilled and helping to repair faulty Web sites – it allows to detect incorrect and incomplete/missing Web pages

Web Site Denotation A web page is a ground term. Consequently, we represent a Web Site as a finite collection of ground terms of a suitable term algebra A web page is a ground term. Consequently, we represent a Web Site as a finite collection of ground terms of a suitable term algebra member( member( Peter name(“Peter”) Peter name(“Peter”) Hawkins surname (“Hawkins”) Hawkins surname (“Hawkins”) Professor status (“Professor”) Professor status (“Professor”) teaching( teaching( Algebra course (“Algebra”) Algebra course (“Algebra”) ) )

Specification Language A Web specification is a triple (R, I N, I M ) where A Web specification is a triple (R, I N, I M ) where – R is a set of user´s function definitions – I N is a set of correctNess rules – I M is a set of coMpleteness rules

Specification Language Correctness Rules A correctness rule has the following form: A correctness rule has the following form: l -> error | C where - l is a term - l is a term - error is a reserved constant - error is a reserved constant - C is a sequence of equations and membership tests w.r.t. regular languages - C is a sequence of equations and membership tests w.r.t. regular languages e.g. project(year(X)) -> error | X in [0-9]*, X error | X in [0-9]*, X<1990

Specification Language Completeness Rules A completeness rule has de following form: A completeness rule has de following form: l -> r where - l is a term - l is a term - r is a term s. t. Var(r) ⊆ Var(l) - r is a term s. t. Var(r) ⊆ Var(l) e.g. member(name(X),surname(Y))->hpage(name(X),surname(Y),status())

Specification Language Completeness Rules Some symbols in the right-hand side of the rules can be marked by symbol # Some symbols in the right-hand side of the rules can be marked by symbol # Marks are used to select the Web pages on which we want to check a given condition. Marks are used to select the Web pages on which we want to check a given condition. l -> #r e.g. hpage(status(“Professor”) -> #hpage(#status(#“Professor”),teaching)

Rule Interpretation Correctness Rules Correctness Rules l -> error | C if l is recognized in some Web page of W and all the expressions represented in C are evalutaed to True (or C is empty), the web page is incorrect Completeness Rules Completeness Rules l -> #r if l is recognized in some Web page of W, then r must be recognized in some Web page of W which contain the marked part of r

An Example… … first of all, some GVerdi details to be considered: * XML/XHTML Web Pages * Function definitions of R are written in Haskell and saved in the file Defs.hs. Haskell functions which are defined in the Prelude standard library are available too. * wxHaskell-0.8, RegexpLib98 and hxml-0.2 * wxHaskell-0.8, RegexpLib98 and hxml-0.2

Conclusions We presented the system GVerdi We presented the system GVerdi – Written in Haskell – 1100 lines of code (approx.) – Parser for web pages and specifications – Partial Rewriting, Verification Technique and Graphical User Interface We are able to detect missing/incomplete and incorrect Web pages efficiently We are able to detect missing/incomplete and incorrect Web pages efficiently

Future Work Improving Regular Expressions capabilities Improving Regular Expressions capabilities Verification of full XML code (namespaces, attributes, etc.) Verification of full XML code (namespaces, attributes, etc.) Moving towards the verification of dynamic Web sites Moving towards the verification of dynamic Web sites

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