Verifying Software Requirements with XSLT

ACM SIGSOFT So wa e Enginee ing No es ol 27 no 1 Ve i ying So wa e Requi emen s wi h XSLT Amado Du n, An onio Ruiz, Bea iz Be n~ dez and Miguel To o Depa men o Compu e Languages and Sys ems Uni e si y o Se ille, Spain e-mail: {amado ,a uiz,bea ,m o o}@lsi.us.es Janua y 2002 Page 39 Abs ac In his a icle, we p esen an app oach o he au oma ic e - i ica ion o so wa e equi emen s documen s. This app oach is based on he ep esen a ion o so wa e equi emen s in XML and he usage o he XSLT language no only o au o- ma ically gene a e equi emen s documen s, bu also o e i y some desi ed quali y p ope ies and o compu e some me ics. These ideas ha e been implemen ed in REM, an expe imen al equi emen s managemen ool ha is also desc ibed in his pape . Keywo ds: equi emen s enginee ing, equi emen s e i i- ca ion, XML, XSLT In oduc ion Pa aph asing Boehm [5], equi emen s alida ion and e - i ica ion can be in o mally de ined by he ques ions "Am I building he igh equi emen s?" ( alida ion) and "Am I building he equi emen s igh ?" ( e i ica ion). In o he wo ds, he goal o equi emen s alida ion is o ensu e ha equi emen s documen s con ain ac ual equi e- men s and ha hese equi emen s a e all he known equi e- men s by he ime he equi emen s documen s a e baselined. On he o he hand, he goal o equi emen s e i ica ion is o ensu e he quali y o equi emen s acco ding o desi ed quali y p ope ies. Some o hese quali y p ope ies ha e o do wi h equi emen s seman ics bu o he s ha e o do wi h syn ac ic, s uc u al o p agma ic aspec s o equi emen s (see [12] o a comple e classi ica ion o quali y p ope ies o equi emen s). Ve i ica ion o seman ic p ope ies o equi emen s is closely ela ed o equi emen s alida ion 1 and equi es hu- man pa icipa ion, whe eas e i ica ion o non-seman ic p ope ies should be as au oma ed as possible. In his a icle, we p esen an au oma ed app oach o he e i ica ion o some quali y p ope ies o equi emen s. Mos o hese p ope ies can be classi ied as non-seman ic, bu we ha e also de eloped some heu is ics o check po en ial p oblems wi h some seman ic p ope ies. Ou app oach is based on he eme gen echnology buil a ound X_ML [4] and i s companion language XSLT [3]. The es o he a icle is o ganized as ollows. Fi s , we b ie ly desc ibe he basics o XML and XSLT needed o un- de s and he ollowing sec ions. Then, we desc ibe REM, an expe imen al equi emen s managemen ool [8, 9], he 1Dis inc ion be ween equi emen s e i ica ion and alida ion is some imes sub le and many au ho s use bo h e ms in e changeably. XML model o equi emen s used by REM and how XSLT can be used o e i y some quali y p ope ies o equi e- men s exp essed in XML. Finally, we discuss some ela ed wo k, p esen some esul s and poin ou u u e wo k. XML and XSLT XML Basics The e a e millions o web pages w i en in HTML a ailable in In e ne . In hese web pages, pu e in o ma ion is mixed wi h o ma ing elemen s, making he au oma ic p ocessing o in o ma ion e y di icul . XML [4] is a language designed o ep esen ing pu e in o ma ion in In e ne . In o ma ion in XML is ep esen ed by elemen s. An XML elemen is made up o a s a ag, an end ag, and o he ags o da a in be ween. Fo example, o ep esen ing he in o ma ion abou a book, we migh ha e he ollowing XML elemen named book: <book isbn="X-XXX-XXXX-X"> <au ho >Misuel de Ce an es</au ho > < i le>E1 Quijo e</ i le> </book> As you can see, he in o ma ion abou a book is be ween he ibookL and j/bookL ags and i is easy o pa se by a com- pu e p og am. The au ho and i le elemen s a e conside ed as child en o he book elemen , hus o ming a hie a chy. An XML documen mus always ha e one and only one oo elemen a he op o i s hie a chy. In o de o allow in o ma ion in e change be ween wo o mo e pa ies using XML, hey mus ag ee abou elemen g amma and seman ics. Elemen g amma is speci ied as egula exp essions in DTDs (Documen Type De ini ions) [4]. Fo example, he DTD agmen o he p e ious XML da a would be he ollowing: <!~T~MENTbook (au ho +, i le)> <!ATTLIST book isbn ID #REQUIRED> <!ELEMENT au ho (#PCDATA)> <!~T~MENT i le (#PCDATA)> whe e i is s a ed ha a book elemen can con ain one o mo e au ho elemen s and only one i le elemen . An XML elemen can also ha e a ibu es. Fo example, isbn is de ined as a equi ed iden i ica ion a ibu e o book, i.e. he e canno exis wo books wi h he same alue o he isbn a ibu e in he same XML documen . Those elemen s ha con ain only ex a e said o con ain #PCDATA, ha s ands o pa sed cha ac e da a. ACM SIGSOFT So wa e Enginee ing No es ol 27 no 1 Janua y 2002 Page 40 T ans o ming XML The e a e many si ua ions in which XML da a need o be ans o med. Fo example, o p esen ing XML da a as an HTML page. XSLT [3] is a language based on ans o ma- ion pa e ns. An XSLT s yleshee , which is also a an XML documen , sea ches o pa e ns in he XML da a and applies p og ammed ans o ma ions, hus gene a ing some ou pu esul s. Fo example, i we wan ed o show in o ma ion abou books in a web b owse , we could apply he ollowing XSLT ans o ma ion ule: <xsl : empla e ma ch="book"> <B><xsl : alue-o ~elec =" i le"/></B> (ISBN <xsl: alue-o selec ="©isbn"/>) was w i¢¢en by <EM><xsl: alue-o selec ="au ho [1] "/></EM> </xsl : " empla e> The in o mal seman ics o his XSLT ule a e "when you ind a book elemen , gene a e i s i le in bold ace, hen i s ISBN a ibu e (no ice he @ p e ix o a ibu es), and hen i s i s au ho in emphasized mode". In he XSLT code, ex li e als like TML ags can be mixed wi h elemen alues, which a e ob ained by means o he xsl: alue-o s a emen . I we applied his XSLT ule o he p e ious XML da a, he esul o he ans o ma ion would be some hing like his when ende ed in a web b owse : E1 Quijo e (ISBN X-XXX-XXXX-X) was w i en by Miguel de Ce an es Al hough he e a e many mo e de ails abou XML and XSLT, we hink ha his b ie in oduc ion should be enough o hose eade s no amilia wi h XML echnologies in o de o unde s and he es o his a icle. REM: An XML-based Requi emen s Managemen Tool REM (REqui emen s Manage ) is an expe imen al equi e- men s managemen ool de eloped by one o he au ho s [8, 9]. In REM, a equi emen s enginee ing (RE) p ojec is conside ed o be composed o h ee documen s: 1. a cus ome -o ien ed equi emen s documen ( he equi e- men s documen [13]), usually con aining equi emen s in na u al language exp essed in e ms o cus ome 's ocab- ula y, also known as C- equi emen s [7]. 2. a de elope -o ien ed equi emen s documen ( he speci- ica ion documen [13]), usually con aining equi emen s models and mo e echnical in o ma ion, also called D- equi emen s [7]. 3. a egis y o de ec ed con lic s and nego ia ion suppo . In REM, C- equi emen s and con lic s a e exp essed in na u al language using p ede ined equi emen s empla es and some linguis ic pa e ns (see [9] o de ails). Fo exp ess- ing D- equi emen s, we ha e chosen a subse o he UML [6] REM A chi ec u e REM documen s, i.e. RE p ojec s composed o he h ee doc- umen s p e iously desc ibed, a e s o ed in ela ional ligh - weigh da abases. When he use c ea es a new REM docu- men , he basic s uc u e is aken om a REM base documen (see igu e 1), ha can be emp y o can con ain he manda- o y sec ions o so wa e equi emen s s anda ds like [1] o [15]. Any o dina y REM documen can be selec ed as a base documen , so use s can c ea e hei own base documen s o euse o he REM documen s. Eng nee /-s~# l ~ X~ da a | I ~ I uJu[ [ ~ yj ~sne LIJ ob ec s Enginee ing P ojec s ~ ~ ' (MDB o ma ) Figu e 1: REM A chi ec u e In o de o p o ide immedia e eedback on use ac ions, REM gene a es XML da a co esponding o he documen being edi ed, applies an ex e nal XSLT s yleshee ha ans- o ms XML da a in o HTML and shows he esul ing HTML o he use . In his way, whene e he use changes a equi e- men s documen , he o she can see he e ec s immedia ely. In a simila way he REM base documen can be ailo ed, he use can also change documen appea ance by selec ing o c ea ing di e en ex e nal XSTL s yleshee s. The de aul XSLT s yleshee gene a es a highly hype linked documen , easing na iga ion o equi emen s documen s (see igh side o igu e 2). O he con igu able aspec o REM is he language o he use in e ace. The use can choose i by selec ing an ex e - nal esou ce dynamic link lib a y (DLL). A he momen o w i ing, we ha e de eloped wo ex e nal esou ce DLLs o REM, one in Spanish and o he in English. Ano he one in Po uguese is unde de elopmen . REM Use In e ace The use in e ace o REM p esen s wo di e en iews o he use (see igu e 2). On he le , he use can see a abbed iew wi h h ee ee iews, one o each equi emen s documen in he RE p ojec . On he igh hand, he esul o he XSLT ACM SIGSOFT So wa e Enginee ing No es ol 27 no 1 3anua y 2002 Page 41 [:~j..<~ 3.1 Capabili y equi emen s ~.-~iii!~;~ 3.1.1 Sys em ac o s i % ~ ac -000~ Cos ome • :~ i,....;~ [ACT-O002] Employee ~-.~ 3.1.2 In o ma ion s o age n ~],.l~ [IRQ-O001] In o ma ion :, i$' ,[XRq-OOOZ],.~o m~Uon ~1--1 ~ [IRQ-O003] In o ma ion [] "'~!~i~ 3. ~ Z_Sy~. e_ g~se cg.~eP. .... i.....~ I. Ac o Cus ome asi~ !.....'~ 2, Ac o Employee q ~ • i~ :.~ i "~yT"~, 3, The sys em showsi~ : i L,. ~l~ I he e a e no a~ !.,.--% 4, Ac o Cus ome chl I i..--., 5. Ac o Employee as I : . O dh a D, llex i iThe sys em shall beha e as de sc ibed in. he ollo~.~..~.~..~ .................. ~[when a cus ome wan s o en . a C~ .......... ............. ................. e i/q--![Ac o, Cu~oms* (ACT-OOOD asks 0, a a~lable ca s o !i * ~_l~yJ.~.2~.~..~.~i que ies he sys em o sys em shows a lis o a ailab!e ¢~s ......................................... chooses one a ailable ca asks 0s ~en .a! da es cus 0ms da a o he p o ides ~ da es and .~ .em .~ ~.. ..°_. .~.~..°.~L~d.:e~s. .~_~ .~ ~.. _...i me_._~ has en ed he ca s i!i Figu e 2: REM Use In e ace ans o ma ion o he XML da a is p esen ed o he use in a embedded web b owse . In any o he h ee ee iews, he use can di ec ly manip- ula e objec s by d ag and d op o by con ex menus. Only ac ions ha ha e sense can be pe o med, ollowing a co ec - by-cons uc ion app oach, hus inc easing quali y and sa ing e i ica ion e o . Fo example, ac ions o use case s eps can be o h ee di - e en classes (see igu e 4): ac o ac ion, i he ac ion is pe o med by an ac o ; sys em ac ion i he ac ion is pe - o med by he sys em, o use case ac ion, i he ac ion con- sis s o pe o ming o he use case, i.e. an use case inclusion o ex ension [6]. Ac o ac ions and use case ac ions can be c ea ed only i some ac o o some use case ha e been p e i- ously c ea ed. In gene al, objec s can be c ea ed by means o con ex menus on po en ial pa en s o by means o he c ea ion oolba . XML Model o Requi emen s in REM REM is based on an UML [6] model o equi emen s (a pa ial iew o his model is shown in igu e 4). The main objec class o he model is he Requi emen s Documen , ha is composed o a sequence o REM objec s. See igu e 3 o a classi ica ion o REM objec s. We ha e ansla ed ou UML model o equi emen s in o a ela ional schema and in o a DTD. As an example, he Use- Case class in igu e 4 has been ansla ed in o he ollowing DTD elemen de ini ion: <!RIRblENT em:useCase ( am:name, am: e sion, am:au ho s?, am:sou ces?, em:commen sT, am:impo ance, am:u gency, am:s a us, am:s abili y, em:isAbs ae ?, em: igEe inEE en , am:p econdi ion, em:pos condi ion, am: equency, em:s~ep* )> <!ATTLIST em:useCase old ID #REQUIRED> Many o he elemen s in he p e ious DTD agmen (commen s, igge ingEe en , p e and pos condi ion), con ains only ex , i.e. na u al language. In REM, ex can be com- posed o any combina ion o ee ex , e e ences o o he objec s and TBD (To Be De e mined) ma ks, de ined as ol- lows: <!ELEMENT em: ex (#PCDATA[ em: e l em: bd)*> <!ELEMENT am: el (#PCDATA)> <!ATTLIST am: el oid IDREF #REQUIRED> <!w~ENT em: bdEMPTY> whe e he em: e elemen mus ha e a equi ed a ibu e called oid ha i is decla ed as an IDIREF, i.e. a e e ence o o he elemen wi h a ma ching iden i ica ion a ibu e alue. An IDREF a ibu e is e y simila o a o eign key in ela- ional da abases. ACM SIGSOFT So wa e Enginee ing No es ol 27 no 1 Janua y 2002 Page 42 REM objec , Sec ionappendix Pa ag aphglossa yi em Ex em~lg aphic ile T aceabili yma ix S akeholde s- ela ed objec O ganiza ion S akeholde Mee ing C-Requi emen Objec i e Ac o In o ma io.ns o ag.e equi emen Cons ai l equi emen Func ion .l equi emen. useeas¢ Non unc ion~l equi em ea D-Requi emen l Objeq ype Valu.e ype Associa io.n ype Sys em ope a ion Con lic Figu e 3: Classi ica ion o objec s in REM The em: bd elemen is decla ed as an EMPTY elemen , i.e. i canno ha e nei he subo dina e elemen s no da a. I is simply a ma k. Using XSLT as a Requi emen s Ve i- ica ion Language In he ollowing sec ions we desc ibe how some o he quali y ac o s desc ibed in [10 can be au oma ically e i ied using XSLT when equi emen s a e elec onically s o ed in XML o ma acco ding o he REM DTD. Unambigui y A equi emen is unambiguous i and only i has only one pos- sible in e p e a ion [1]. Ob iously, his is a seman ic p op- e y o a equi emen and canno be au oma ically e i ied, bu we can gi e some hin s abou po en ial ambigui ies in a equi emen s documen . We ag ee wi h Lei e [11] in he impo ance o unde s and- ing he language o he p oblem and in he impo ance o building a glossa y (called Language Ex ended Lexicon, LEL, in [11]). Following Lei e, he glossa y should ollow wo p inciples: he p inciple o ci cula i y, ( he glossa y mus be as sel -con ained as possible) and he p inciple o min- imal ocabula y (use as much glossa y i ems as possible in S akeholde ~ REMObJec , s°u cd~l , I =oo i ~[c°m nen~ C-Requi emen impodance~ u gency~ s a u~ s abili y~ ..................... _L ...... UseCase • I ~Iep ~ -Y----7~--, I -- ~ " V_ "loesc lp '° ~] isAbs a~ . {° demd~L--T~l~---] * i-- lgga ingE en [ • [ ~1 = .... ,,__ p econdi ion] ~;=~ ~ .... p ..... pos condi io ~ ~'~--~ ~ desc ip io~ equency~ I ~'"~" [~ e mina ion~ ----~----~ .... ~ ...... 1 I UseCaseAc lon I Sys emAc ion ! Ac o Ac lon desc ip ion~ [ desc ip ion~ pe o manoe~ ", *~ , Ac o Figu e 4: UML model o use cases in REM you equi emen s desc ip ions). Lei e's p inciples canno gua an ee unambigui y, bu hey can help o build unam- biguous, unde s andable, e i iable, consis en , concise, and c oss- e e enced equi emen s [10]. XSLT can be used o measu e glossa y ci cula i y (GLC) and minimali y o ocabula y (MOV). GLC can be measu ed as he a io be ween glossa y i ems and e e ences o glossa y i ems om o he glossa y i ems. The ollowing XSLT code, whe e we ha e decla ed a a iable o he sake o eadabili y, can be used o compu ing GLC: <xsl : a iable name="GLC" selec ="coun (// em:glossa yI em) di coun (// em: glossa yI em// em: e ) "/> <xsl : alue-o selec =" o ma -numbe ($GLC, ' #0. O0 ~ ) "/> whe e he exp ession // em:glcx~sa yl em is an X.Pa h exp ession [2] meaning "any em:glossa yl em ele- men descendan o he oo ", whe eas he exp ession // e n:giossa yl em// em: e means "any em: e elemen descendan o any em:glossa yi em descendan o he oo ". In XPa h, he language o building na iga ion exp essions o e XML ees, an elemen is conside ed as descendan o o he elemen i i is i s child a any le el o dep h in he hie a chy. A simila a io be ween he numbe o e e ences o glos- sa y i ems in equi emen s and he numbe o equi emen s can be used o measu e MOV. F om he MOV iewpoin , ACM SIGSOFT So wa e Enginee ing No es ol 27 no 1 Janua y 2002 Page 43 i is also possible o de ec hose "suspicious" equi emen s ha do no ha e any e e ence o any glossa y i em in hei ex . Since hose equi emen s a e no using he ocabula y o he cus ome , hey should be checked o po en ial p ob- lems o ambigui y o unde s andabili y [10]. Fo example, i we wan o know which use cases a e "suspicious", we can use he ollowing XSLT code: <xsl : empla e ma ch " em:useCase [no (.// em: e )] "/> U~e case <xsl : alue-o selec =" em:name"/> does no use any glossa y i em </xsl : empla e> whe e he ma ch exp ession uses b acke s o selec only hose use cases wi h no descendan e e ences. Ano he possibili y is o de e mine a h eshold alue o he num- be o e e ences pe equi emen and conside as suspi- cious all equi emen s wi h a numbe o e e ences unde he h eshold. In ha case, he ma ch exp ession would be em:useCase[coun (.// em: e ) i m], wi h m being he MOV h eshold. Comple eness A equi emen s documen is comple e i i includes [10]: 1. E e y hing ha he so wa e is supposed o do, i.e. all he equi emen s 2. Responses o he so wa e o all classes o inpu da a in all ealizable si ua ions 3. Page numbe s, igu e and able names and e e ences, a glossa y, uni s o measu e and e e enced ma e ial 4. No sec ions ma ked as TBD In ou app oach, he hi d comple eness condi ion is pa - ially sa is ied by means o he co ec -by-cons uc ion pa a- digm o REM: igu e and able names a e au oma ically gen- e a ed, e e ences a e au oma ically inse ed and upda ed, and he use can easily c ea e a glossa y. I we wan o be su e abou he exis ence o a sec ion named Glossa y, we can apply he ollowing XSLT code: <xsl: choose> <xs i :when es ="// am: sec ion [ am: name=' Glossa y ' ] "/> The e is a glossa y </xsl: when> <xsl : o he wise> The e is no glossa y </xsl : o he wise> </xsl : choose> whe e he s uc u e o med by xsl:choose, xsl:when and xsl:o he wise is basically an i -else-endi s a emen wi h mul- iple else b anches. No ice ha i we wan o check he ex- is ence o an elemen we canno use an XSLT empla e. I he e is no such an elemen , he empla e will ne e ma ch and we will ha e no ou pu . Simila XSLT code can be used o e i y i equi emen s documen s a e o ganized [10], i.e. i hey ha e manda o y sec ions in he manda o y o de wi h manda o y con en . The ou h condi ion o comple eness, he absence o TBD ma ks, can be easily e i ied using XSLT. I we wan o know how many TBD ma ks a e in a equi emen s documen we can apply he ollowing X_LST code: The e axe <xsl : alue-o selec =" coun (// am: bd) "/> TBD ma ks ha would gene a e in he ou pu he numbe o occu ences o elemen s o ype em: bd anywhe e in he XML da a. I we wan o be mo e p ecise and we wan o know wha use cases ha e TBD ma ks inside hei ex and how many TBD ma ks hey ha e, we could w i e he ollowing XSLT code: <xsl : empla e ma ch=" em:useCase [./I em: bd] "/> Use case <xsl: alue-o selec =" em:name"/> has <xsl: alue-o selec =" coun (.// am: bd) "/> TBD ma ks </xsl: empla e> in which he selec exp ession " em:useCase[.// em: bd]" means "any use case wi h a leas one descendan o ype em: bd". T aceabili y In [10], a equi emen s documen is said o be aceable i and only i i is w i en in a manne ha eases he e e - encing o each indi idual equi emen . Since REM assigns au oma ically an unique iden i ie o e e y equi emen ( he equi ed iden i ie a ibu e oid, see he DTD o use cases), his quali y ac o does no ha e o be e i ied explici ly. Wha i nms be checked is i he o igin o e e y equi e- men is clea , i.e. i equi emen s a e aced [10]. In ou UML model o equi emen s, any REM objec can be aced o and om o he REM objec s and o hei human sou ces and au- ho s (see igu e 4). Checking i a equi emen has sou ces and au ho s and i i is aced o o om o he equi emen s is easy wi h XSLT. Fo example, he ollowing XSLT em- pla e will ma ch all use cases wi h no human sou ces: <xsl : empla e ma ch " em: useCase [no ( am: sou ces) ] "> Use case <xsl: alue-o selec =" em:name"/> has no sou ces </xsl: empla e> And his XSLT empla e will ma ch all non unc ional e- qui emen s no aced o o he REIV1 objec s: <xsl : empla e ma ch=" am: nonFunc ionalRequi emen "> <xsl:i es "no (// em: ace[©sou ce=cux en ()/©oid])"> Non unc ional equi emen <xsl : alue-o selec =" em: name"/> is no aced o any objec </xsl: i > </xsl : empla e> ACM SIGSOFT So wa e Enginee ing No es ol 27 no 1 Janua y 2002 Page 44 In REM, aces a e de ined as elemen s wi h wo equi ed a ibu es o ype IDREF, namely sou ce and a ge . The use o REM can also use aceabili y ma ices o isual checking o non- aced equi emen s. O he e i iable quali y ac o s Applying he same ideas, o he quali y ac o s de ined in [10] can be e i ied using XSLT, o example: • Wha equi emen s a e no anno a ed wi h ela i e im- po ance, ela i e s abili y o e sion. * Wha equi emen s ha e po en ially ambiguous wo ds in hei desc ip ion, like easy o, use - iendly, e c. by means o XSLT s ing unc ions like con ains [3]. • I use cases a e no well s uc u ed, i.e. i he e a e oo ew o oo many includes o ex ends ela ionships. • Wha use cases ha e oo ew o oo many s eps, o oo much excep ions, i.e. oo many al e na i e cou ses. • Wha de ined ac o s do no pa icipa e en any use case. Rela ed Wo k Mos wo k on au oma ed equi emen s e i ica ion is based on Na u al Language P ocesssing (NLP), like [14] o [12]. Those app oaches, ocused on seman ic analysis o equi e- men s, usually make equi emen s enginee s w i e equi e- men s in a subse o na u al language, demand many com- pu e esou ces and ha e no been widely adop ed in indus- y. The Au oma ed Requi emen Measu emen (ARM) ool [16], is p obably he mos ela ed wo k o he app oach p e- sen ed in his a icle. I is a simple ye powe ul ool ha scans equi emen s documen s sea ching o indica o s, i.e. wo ds ha ha e been iden i ied as indica o s o good o bad quali y p ope ies. Ou app oach does no use NLP bu an open, simple and ligh e echnology like XML/XSLT. We can o e he same unc ionali y o ARM plus all addi ional e i ica ion desc ibed in his pape , and he use o REM can de ined his o he own XSLT e i ica ion s yleshee s. F om a p ac ical poin o iew, we hink ha ou esul s a e use ul o he a e age equi emen s enginee . Conclusions and Fu u e Wo k In his a icle we ha e b ie ly p esen ed an au oma ed ap- p oach o he e i ica ion o so wa e equi emen s. Ou ap- p oach is based on a open echnology like XML and XSLT. In ac , i equi emen s a e ep esen ed in XML using a di - e en DTD, many o he XSLT code p esen ed in his pape should be easily adap ed. Ou app oach does no need ha d compu e esou ces and i has p o ed o be use ul when used wi h ou s uden s a he Uni e si y o Se ille. Ou u u e wo k is ocused in de eloping quali y me ics, so we can de ec po en ial p oblems wi h equi emen s com- pa ing quan i a i e alues. We expec o iden i y some use ul me ics soon by applying da a mining echniques o he e- qui emen s documen s gene a ed by ou s uden s. Acknowledgmen s This wo k is pa ially unded by he Spanish CICYT p ojec GEOZOCO TIC 2000-1106-C02- 01 and by he in e na ional CYTED p ojec WEST. Re e ences [1] IEEE Recommended P ac ice o So wa e Requi emen s Speci ica ions. IEEE/ANSI S anda d 830-1998, Ins i u e o Elec ical and Elec onics Enginee s, 1998. [2] XML Pa h Language (XPa h) 1.0. W3C Recommenda ion, No embe 1999. [3] XSL T ans o ma ions (XSLT) 1.0. W3C Recommenda ion, No embe 1999. [4] Ex ensible Ma kup Language (XML) 1.0 (Second Edi ion). W3C Recommenda ion, Oc obe 2000. [5] B. W. Boehm. 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