Validation of XML Document Updates based on XML Schema in XML Databases * Sang-Kyun Kim 1, Myungcheol Lee 2 and Kyu-Chul Lee 1

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1 Vlidtion of XML Document Updtes sed on XML Schem in XML Dtses * Sng-Kyun Kim 1, Myungcheol Lee 2 nd Kyu-hul Lee 1 1 Dept. of omputer ngineering, hungnm Ntionl University, KORA {skkim,kclee}@ce.cnu.c.kr 2 omputer System Deprtment, omputer & Softwre Reserch Lortory, lectronics nd Telecommunictions Reserch Institute, KORA mclee@etri.re.kr Astrct. We study the vlidtion of XML documents when they re updted in XML dtses. An XML document cn e verified y checking ginst n XML Schem, which contins structure nd type informtion of XML documents. owever, most of XML dtse systems just vlidte the whole XML document, ut cn not vlidte prts of it. If updtes re very frequent, then vlidting the whole XML document will cuse serious performnce degrdtion. Furthermore, rollck should e performed if the updtes result in n invlid document, ecuse the updted document is usully vlidted fter the updte opertion executed. In this pper, we propose n immedite nd prtil vlidtion mechnism for solving these two prolems, i.e the vlidity of n updte opertion is checked immeditely efore the ctul updte is pplied to the dtse whether it cuses invlidity, nd vlidtion is performed only on the updted prts of the XML document in the dtse. onsequently, XML dtse systems cn mintin vlid XML documents t ny time. We lredy proposed n immedite nd prtil vlidtion mechnism sed on DTD[6], nd we extend the mechnism sed on XML Schem in this pper. 1 Introduction Since XML hs emerged s the Internet electronic document stndrd for neutrl dt representtion nd exchnge, mny reserchers nd dtse vendors hve studied efficient wys to fcilitte the tsk of storing nd querying XML documents. The next step to leverge XML into full-fetured Internet dt formt is to support updtes nd their vlidtion. Recently, severl reserches[1][2][3] hve een performed for updting XML documents. These studies define updte opertions y extending XQuery nd try to resolve semntic prolems occurring during the process of the updte opertions. owever, two or more updte opertions in single updte sttement could cuse severl conflict prolems in these pproches, ecuse the updte opertion is usully vlidted fter execution. For solving these conflicts, when n XML document in the dtse is updted, XML dtse systems must e le to vlidte immeditely the updte opertion with respect to XML Schem efore it is executed. ence, only when the opertion is vlid, it is executed. * This work ws prtilly supported y Brin Kore (BK) 21 nd Softwre Reserch enter (SOR) in hungnm Ntionl University, Kore

2 Whenever ppliction progrms modify n XML document, the XML prser must check the whole document for the vlidtion. owever, this is very inefficient in cse tht frequent updtes occur upon smll portions of documents. It ecomes more serious when XML documents re stored in dtse thn in file. To vlidte n XML document modified y the updte opertions, we must tke out the whole XML document nd its schem informtion from the dtse, nd then pss them to prser to check the vlidity so tht vlidtion time my result in serious performnce degrdtion. owever, most of the XML document updte mechnisms use the full vlidtion pproch, ecuse there hve een few mechnism to support the prtil vlidtion until now. Recently, severl efforts hve een progressed for more efficient hndling of the XML document vlidtion. hen [] provides wy to gurntee tht vlid XML views re defined, ut updtes nd their vlidtion for XML views re not considered. Ppkonstntinou [5] suggests n incrementl vlidtion lgorithm of XML documents. This mechnism enles the prtil vlidtion ut it is prolemtic ecuse the uxiliry structure must e recomputed whenever n updte opertion is performed. In section, we discuss this lgorithm in detil. We hve lredy studied vlidtion mechnism sed on DTD[6], which supports immedite vlidtion of only updted prts when n XML document stored in the dtse is updted. In this pper, we extend our previous work to the vlidtion mechnism sed on XML Schem. Our pproch is performed on inserts, deletes nd updtes of elements. For efficient vlidtion, we trnslte XML schem informtion into set of deterministic finite utomton (DFA)[7], nd store DFAs into dtse tle. Thus, when n XML document stored in the dtse is updted, we cn immeditely check the vlidity of only updted prts using the stored schem informtion efore it is ctully pplied to dtse. The reminder of this pper is orgnized s follows. In section 2, we define the vlidtion frmework. In section 3, we present our mechnism to vlidte immeditely prts of n XML document in the dtse. In section, we discuss prior efforts for the relted sujects nd compre our mechnism with them. Finlly, in section 5, we summrize this pper. 2 Vlidtion Frmework An XML document contins its own structurl informtion. Therefore, efore we store XML documents into the dtse or updte them in pplictions, we must verify tht the structurl informtion is vlid. In the following, we define the vlidtion of XML documents sed on vlidtion grnulrity nd vlidtion time: Definition 1 The vlidtion sed on vlidtion grnulrity is defined s follows. - The full vlidtion of n XML document is to vlidte the whole document. - The prtil vlidtion of n XML document is to vlidte only updted prts of the XML document

3 Definition 2 The vlidtion sed on vlidtion time is defined s follows. - The deferred vlidtion of n XML document is to perform vlidtion fter updting. - The immedite vlidtion of n XML document is to perform vlidtion efore updting, nd updtes re executed only if it is vlid. Most of XML dtse systems use deferred nd full vlidtion method in cse XML documents re updted. As we descried in section 1, this method hs conflicts nd performnce prolems for updte opertions. Therefore, for solving these prolems, XML dtse systems must e le to support immedite nd prtil vlidtion method so tht they cn lwys mintin vlid XML documents efficiently. Typiclly, these vlidtion steps required for the immedite nd prtil vlidtion in XML dtse systems re defined s follows: Definition 3 The vlidtion steps for the immedite nd prtil vlidtion in XML dtse systems re defined s follows: 1. Prse XML Schem files nd extrct their informtion. 2. Store the extrcted schem informtion into the dtse. 3. When n XML document updted, check its vlidity y referencing the stored schem informtion.. Perform the updte opertion or not ccording to the vlidity. In the next section, we pply these vlidtion steps to the vlidtion of XML documents with respect to XML schem to perform the immedite nd prtil vlidtion. 3 Immedite nd Prtil XML Schem Vlidtion 3.1 xpression of the XML Schem Informtion. An XML document cn e represented y n unrnked tree[8] over finite lphet Σ. Unrnked trees re finite leled trees where nodes cn hve n ritrry numer of children. An unrnked tree over Σ stisfies n XML Schem if the tree is derivtion tree of XML Schem s grmmr, i.e. this tree is vlid with respect to n XML Schem. DTDs re extended context-free grmmrs (F) [9][10][11] in which the righthnd sides of productions re regulr expressions clled content models. The productions of DTD re clled element type definitions. An F is specified y 3- tuple = (Σ,P,S) where Σ is finite lphet tht consists of nonterminl symols N nd terminl symols T, P is finite set of production schems, nd the nonterminl S is the sentence symol. ch production schem in n F hs the form A P, where A N, nd is regulr expression over the lphet Σ = N T. The lnguge L() of n extended context-free grmmr is the set of terminl strings derivle from the sentence symol of. Formlly, L()={w Σ* S + w}, where + denotes the trnsitive closure of the derivility reltion.

4 XML Schems cn e strcted s specilized DTDs[12] tht decouple the type of n element from its lel. A specilized DTD is -typle =(Σ,Σ t,d,µ) where Σ is finite lphet of lels, Σ t is finite lphet of types, d is DTD over Σ t nd µ is mpping from Σ to Σ t. The lnguge L( ) of specilized DTD is the set of terminl strings over the lphet of types Σ with respect to extended context-free grmmr. Formlly, L( )={w Σ*,w t Σ t * µ(w t )=w} In this pper, we use the DFA of finite utomt to recognize the regulr expression. The finite utomt re clssified into nondeterministic finite utomt(nfa) nd DFA. Both cn recognize exctly wht regulr expressions cn denote through generlized trnsition digrms. owever, there is difference in tht DFA hs t most one trnsition while NFA my hve severl trnsitions from ech stte on ny input. Therefore, DFA is suitle rther thn NFA to support the prtil vlidtion which only modified prts must e vlidted, since there is t most one pth from the strt stte leled y tht string. We do not suggest here ny concrete lgorithms to express the mpping from Σ to Σ t in XML Schem. This could e implemented in vrious wys. For exmple, the type informtion of Σ t cn e stored s the userdefined dttype of dtse system, nd vlidted y the own type-checking mechnism of the dtse system when n updte opertion occurs. 3.2 onstruction of DFA Mny studies hve een proposed for constructing finite utomt from regulr expressions[7][13][1][15]. To construct DFA from regulr expression, we first could construct NFA using Thompson construction[1] or lushkov construction[15], nd trnslte them into DFA using Suset construction. Alterntively we could directly trnslte regulr expression into DFA[7]. A DFA constructed y ove methods cn recognize string of lnguge, ut cn not recognize only the sustring of string. owever, we need to recognize only the sustring modified y updtes to support efficient prtil vlidtion. Thus, we propose n lgorithm to construct DFA from regulr expression to support the prtil vlidtion. This lgorithm uses the syntctic structure of regulr expressions to guide the construction process. We show how to construct DFA for regulr expressions tht hve lterntion, conctention nd unry postfix opertor. Definition If Σ nd Σ re symols, then nd lso could e regulr expressions tht denote L()={} nd L()={} respectively. Definition 5 Suppose nd re regulr expressions denoting the lnguge L()={} nd L()={} respectively, the lnguge L() defined y regulr expression over Σ is defined inductively s follows: - L() = L()L() - L( ) = L() L() - L(*) = {v 1...v n v 1,...,v n L(), n 0} - L( + ) = {v 1...v n v 1,...,v n L(), n 1} - L(?) = L() {ε}, where the symol ε denotes the null string - L({p,q}) = {v 1...v n v 1,...,v n L(), p n q}

5 Algorithm 1 : onstructing DFAs Input : A regulr expression over n lphet Σ Output : A DFA D ccepting L() Steps : 1. Prse into its constituent suexpressions. 2. For ech of six opertors in definition 5, construct DFAs s follows. (for ech i, 0<i<n, Σ nd Σ re symols) strt L() i i+1 L( ) strt i strt L({p,q},) i i+1 {p,q} i+2 i+1 i+2 strt L(?,) i i+1 strt L(*,) i i+1 strt L( +,) i i+1 3. omine DFAs whenever n opertor occurs in n element declrtion until we otin the entire DFA. We just construct DFA per n element declrtion, nd do not comine DFAs for ech declrtion.. onstruct DFA recursively for the prenthesized regulr expression in n element declrtion. We use the following nottion for DFA. A DFA is 5-tuple D = (S,Σ,s 0,F,δ) where S is set of sttes, Σ is finite lphet, s 0 S is strt stte, F S is the set of finl sttes nd δ is mpping from S Σ to P(S). The ove lgorithm constructs DFA for regulr expression of n element declrtion, nd DFA for ech opertor is constructed ccording to the second step of the lgorithm in ech declrtion. Note tht ll of elements with the sme lel in DFA lwys rrive t the sme stte. Formlly, δ(s j-1,i j )=s j, for ech i nd j, s S, i Σ, 0<j<n. Therefore, this property enles us to identify the rrivl stte of n element in DFA so tht we cn esily serch position of the sustring in string of DFA. The prtil vlidtion uses this property. Fig. 1 shows n exmple of constructing DFA for n element declrtion in n XML Schem. <xsd:complextype nme="elementatype"> <xsd:sequence> <xsd:element nme="b" minoccurs="0" mxoccurs="5" type="xsd:string" defult="title"/> <xsd:sequence minoccurs="0" mxoccurs="unounded"> <xsd:element nme="" type="xsd:integer" fixed="37"/> <xsd:element nme="d" type="xsd:integer"/> </xsd:sequence> <xsd:element nme="" minoccurs="5" mxoccurs="10"/> <xsd:element nme="f" minoccurs="0"/> <xsd:choice minoccurs="0" mxoccurs="unounded"> <xsd:element nme="" type="xsd:string"/> <xsd:element nme="" type="xsd:string"/> </xsd:choice> </xsd:sequence> </xsd:complextype> <xsd:element nme="a" type="elementatype"/> Fig. 1 An exmple of n XML Schem i+2 i+2 i+2

6 strt 0 B 1 2 D 3 F 5 6 B{,} {,9} Fig. 2 An exmple of constructing DFA from Fig Storing of DFA The constructed DFAs hve to e stored in the dtse for vlidting updte opertions. For exmple, tle storing the DFA constructed from n XML Schem of Fig. 2 is shown in Fig. 3. We my split ll the trnsitions of DFA for storing in reltionl tle. ch trnsition cn e divided into eforestte, elementnme, fter- Stte, finlstte, minoccurs nd mxoccurs. Then, we store these with schemid, elementnme. By schemid nd elementnme, it is esily identified to which XML Schem nd element declrtion ech tuple reltes respectively. Moreover, there could e other informtion like dt vlues except tht of DFA in n element declrtion. owever we ignore them ecuse their vlidtion is trivil. schemid elementnme eforestte trnnme fterstte finlstte minoccurs mxoccurs pper A 0 B 1 flse pper A 1 B 1 flse unounded pper A 0 2 flse pper A 0 true pper A true 9 Fig. 3 An exmple of storing DFA digrm of Fig Vlidtion of Updte Opertions We introduce here n lgorithm for vlidting n element updte opertion. This lgorithm must e performed efore updtes. onsequently, if it is vlid, the updte opertion will e executed. When vlidting n element updte opertion, it needs not prse the whole document, ut it is sufficient to exmine only three elements, which re the new element to e inserted, previous siling nd next siling of the new element. Becuse we orgnize the schem informtion s ll of elements with the sme nme lwys rrive t the sme stte, we cn esily identify the fterstte of the previous siling element of the new element. Then, we check whether the previous siling element cn e followed y the new element nd the new element cn e followed y the next siling

7 element. owever, it is hrd to serch if there re two or more elements identicl with previous element of inserted element within n element declrtion. Only in this sitution, we exmine whether ll the children re vlid. Inserting n lement. element. Algorithm 2 is vlidting lgorithm for inserting n Algorithm 2 : Vlidtion for inserting n element Input : prent element prentx, previous siling element previousx, n inserted element X, next siling element nextx Output : The nswer "yes" if DFA ccepts X; "no" otherwise Steps : if the dttype of n inserted element X is not vlid then return "no"; if X is declred in n XML Schem then if the regulr expression of prentx == "ny" then return "yes"; else if there re two or more elements hving the sme nme with the previousx then previousx := first child of the prentx; X := next siling of previousx; while ll of children of prentx do if insertvlidtionprocess(previousx, X, null) == flse then return "no"; previousx := X; X := next siling of X; end return "yes"; end if else return insertvlidtionprocess(previousx, X, nextx); end else end if else return "no"; SuAlgorithm : insertvlidtionprocess (check if there exists trnsition in DFA) Input : previous element previousx, n inserted element X, next element nextx Output : The nswer "yes" if there exists trnsition; "no" otherwise Steps : if previousx cn e followed y X then if nextx is exist then if X cn e followed y nextx then return "yes"; else return "no"; end if else return "yes"; end if else return "no"; Fig. shows n exmple of the vlidting process tht conforms to the ove lgorithm when n element is inserted ccording to the element declrtion in the Fig "" is n element declred in n XML Schem. 2. "A", prent element, is not declred s "ny".

8 3. "F", previous element of the inserted element rrives t stte "5".. "", n element to e inserted, cn trnsit from stte "5" to stte "6". 5. "", just next element, cn not trnsit from current stte "6". This insert opertion is not vlid ecuse it cn not stisfy the condition 5. strt <A> <B/> <F/> </> </A> 0 B B{,} 1 2 "" cn not trnsit from stte "6" in cse of inserting "" etween "F" nd "" -> Invlid D 3 {,9} Fig. An exmple of vlidting for inserting n element F 5 6 Deleting n lement. A vlidting lgorithm for deleting n element is similr to tht for inserting. There is difference in tht finl stte must e checked if n element to e deleted is lst element. If ny silings do not hve finl stte t lest fter deleting lst element, it is invlid. Updting n lement. Updting n element cn e simply regrded s the comintion of two processes tht insert n element fter deleting it. Therefore, it is performed to delete first nd insert n element in order. Relted Work Reserches[1][2] for updting XML documents hve defined syntxes for updte opertions nd resolved semntic prolems occurring during the process of the updte opertion. owever, they do not consider how to vlidte updte opertions. Recently, severl efforts hve een proposed for more efficient hndling of XML document vlidtion. hen [] provides wy to gurntee tht vlid XML views re defined. They trnsform n XML document into n Oject-Reltionship- Attriute model for SemiStructured dt (ORA-SS) [16] schem digrm with necessry semntics nd define set of rules to guide the design of vlid XML views. So, vlid XML views could e designed ccording to the guideline, ut updtes nd their vlidtion for XML views re not considered. Ppkonstntinou [5] suggests n incrementl vlidtion lgorithm of XML documents. The incrementl vlidtion is relted with incrementl prsing which hve focused on LR prsing[17][18][19] nd LL prsing[20][21]. The lgorithm strts y prsing the input text nd produces prse tree, which is typiclly nnotted with uxiliry informtion. The uxiliry informtion hs miniml units of the prse tree

9 tht re ffected y the updtes so tht the vlidity of the updtes cn e checked ccording to the uxiliry structures. This mechnism enles the prtil vlidtion, ut it is prolemtic ecuse the uxiliry structure must e recomputed whenever n updte opertion is performed. Therefore, we do not use the incrementl prsing methods in our mechnism. Insted, we extrct nd store the XML Schem informtion through prsing n XML Schem file ccording to our DFA construction lgorithm. This informtion is constructed only once when n XML Schem file is stored into dtse nd need not to e recomputed for vlidting updte opertions. In ddition, Ppkonstntinou [5] provides vlidtion time of O(mlog 2 n) for specilized DTD using n uxiliry structure of size O(n), where m is the numer of updtes in NFA nd n is the size of the document. We hve lredy shown tht our mechnism is lwys etter thn the full vlidting method regrdless of the numer of elements through nlyzing the performnce of updte opertions[6]. In this pper, we compre our mechnism with the incrementl vlidtion of Ppkonstntinou [5]. Like Ppkonstntinou [5], we ssume tht we cn find the prent, the previous siling nd the next siling of n updted element in O(1). Then, the time required for vlidting n updte opertion using our mechnism just ecomes O(3), ecuse it is sufficient to exmine only three elements tht consist of n updted element, previous siling nd next siling of this updted element. owever, if there re two or more elements identicl with previous one of inserting one within n element declrtion, the time required for vlidting is O(m), where m is the numer of silings of the updted element, which is equls to prmeter m of Ppkonstntinou [5]. onsequently, our mechnism shows much etter performnce thn the incrementl vlidtion of Ppkonstntinou [5] 5 onclusion In this pper, we proposed vlidtion mechnism, which supports immedite vlidtion of only updted prts when n XML document stored in the dtse is updted. For this mechnism, we extrct nd store XML Schem informtion. Then, when users updte n XML document stored in the dtse, we verify immeditely whether the updte opertion is vlid or not. onsequently, y using this mechnism for XML dtse systems, they cn lwys mintin vlid XML documents in the dtses s well s resolve the conflict prolems of updte opertions tht could occur for performing updte opertions. In ddition, our mechnism vlidtes three elements t most, new element to e inserted, previous siling nd next siling of this new element without vlidting the whole XML document. Therefore, the vlidtion nd updte process is quite efficient regrdless of the numer of elements within n XML document. Ultimtely, if our mechnism is pplied to XML dtse systems, it cn stisfy users vrious retrievl nd updting requirements. References [1] I.Ttrinov, Z..Ives, A.Y.levy, nd D.S.Weld. Updting XML. Proceedings of AM SIMOD onference, pp.13-2 (2001)

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