On Using Collection for Aggregation and Association Relationships in XML Object-Relational Storage

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1 2004 ACM Symosium on Alied Comuting On Using Collection for Aggregtion nd Assocition Reltionshis in XML Object-Reltionl Storge Eric Prdede, J.Wenny Rhyu Dertment of Comuter Science nd Comuter Eng. L Trobe University Bundoor VIC 3083 Austrli {ekrded, wenny}@cs.ltrobe.edu.u Dvid Tnir School of Business Systems Monsh University Clyton VIC 3800 Austrli Dvid.Tnir@infotech.monsh.edu.u ABSTRACT XML dt cn be stored in different dtbses including Object- Reltionl Dtbse (ORDB). Using ORDB, we get the benefit of the reltionl mturity nd the richness of OO modeling. One modeling concet tht cn be ctured is the collection. Collection structures frequently occur in XML documents esecilly in two reltionshi tyes: ggregtion nd ssocition. However, very often when the dt is stored in dtbse reository, the collection is flttened. We believe tht reserving the collection semntics in the logicl nd the imlementtion level will crete better solution. In this er we roose methods to reserve the collection in XML dt into ORDB using the concet of collection tyes. We use the Semntic Network digrm to reresent the collection of the ggregtion nd the ssocition in XML dt. Ech of these reltionshi tyes will then be trnsformed into storge in n ORDB environment. For ggregtion, we roose different methods bsed on the hierrchy constrint. For ssocition, our method is differentited bsed on the crdinlity. Ctegories nd Subject Descritors H.2.1 [Dtbse Mngement]: Logicl Design dt models Generl Terms Mngement, Design, Theory Keywords XML, XML schem, ORDB, collection 1. INTRODUCTION XML (extensible Mrku Lnguge) is document descrition metlnguge tht is used to reresent lrge-scle dt nd documents in the World Wide Web [11]. For tht reson lone, XML requires efficient dtbse storge to kee its dt. Object-Reltionl Dtbse (ORDB) is incresingly oulr s the dtbse storge for XML Dt [6]. Its oulrity reltes to its bility to cture the object-oriented modeling semntic nd the mturity of the reltionl imlementtion. Mny works hve been roosed to m the Dt Definition Lnguge (DTD) nd the XML Schem into the Object- Reltionl (OR) Schem [6, 7, 12, 13]. These works hve tried to cture different dt structures nd reltionshis tht re exist in XML Documents. One of the structures frequently found in XML Dt is the collection structure. The existing works however, hve med the collections into flt imlementtion model. These rctices hve diminished the concetul level semntic. In ddition, the trnsformtions hve not utilized collection tye in ORDB [8, 9]. These resons hve motivted us to roose different methods of reserving collection in XML Dt into the XML Schem nd the ORDB. We believe tht reserving the concetul semntic in the logicl nd the imlementtion level will crete better solution. Collection in XML Dt cn er in two different reltionshis: ssocition nd ggregtion. While ssocition is defined s reference reltionshi between one to nother object in system, ggregtion is tightly couled form of ssocition [10]. Aggregtion cn be defined s reltionshi in which comosite object ( whole ) consists of other comonent objects ( rts ) [10]. It is the im of this er to roose models tht cn reserve collection for ggregtion nd ssocition reltionshis in XML into ORDB. We erform two ming stes. First is the ming from the concetul model using Semntic Network Digrm to the logicl model using XML Schem. We extend the lgorithm in [3] by roosing different ming methods for ssocition nd ggregtion hierrchy. Second, the logicl model is med into the hysicl imlementtion using SQL in ORDB. For this urose we use the collection dt tyes [8, 9]. Permission to mke digitl or hrd coies of ll or rt of this work for ersonl or clssroom use is grnted without fee rovided tht coies re not mde or distributed for rofit or commercil dvntge nd tht coies ber this notice nd the full cittion on the first ge. To coy otherwise, or reublish, to ost on servers or to redistribute to lists, requires rior secific ermission nd/or fee. SAC 04 Mrch 14-17, 2004, Nicosi, Cyrus. Coyright 2004 ACM /03/04 $5.00. Concetul Model: Semntic Network Model Ste 1 Logicl Model: Ste 2 XML Schem Figure. 1. Ming Stes Physicl Model: ORDB 703

2 2. BACKGROUND In this section we briefly show some existing works on the imlementtion of collection for XML Dt. We lso rovide brief knowledge foundtion on the semntic network model before we use it in our roosed methods. 2.1 Existing Imlementtion in XML Some works hve tried to reserve the design modeling nd to store the XML dt into dtbses tht re bsed on reltionl model including the trditionl reltionl dtbse nd the ORDB. However, there is no work tht utilizes collection dt tyes tht ws introduced by SQL 1999 [5, 9] nd is enriched in SQL4 [8, 9]. Very often when the XML dt is stored in dtbse reository, the collection is not reserved. The collection in ggregtion nd ssocition reltionshi is usully flttened or slit into n entirely serte tble (see Fig.2). [4] resents simle ming of XML dt into the reltionl tbles. In this work, they treted XML documents s grhs with edges nd leves. The edges reresent the reltionshis while the leves reresent the vlues. In this work, the collection ered in ggregtion reltionshi is med into serte flt tbles by using comosite keys. It hs then diminished the collection semntic. [1] rooses comrehensive ming from the DTD into the OO Schem nd the imlementtion of the results into tbles. In the imlementtion stge gin the ggregtion tye is flttened. The ssocition reltionshi is med using IDREF. This is usully done when it is not ossible to form collection or nesting. [11] lso works in the ming of the DTD into the reltionl tbles. They develo n lgorithm nd rototye tht convert the XML documents to tules, trnslte the semi structured XML queries to SQL queries, nd then convert the results to XML dt. This work enlists the limittions of the reltionl dtbse usge for the XML documents. One of those highlights the limittions of imlementing collection semntic in the reltionl tble since this dtbse is unble to hve set-vlued ttributes. [6] rooses ming from the XML Schem into the OO/OR Schem. The work comres how the ming into reltionl schem cn be chnged into the OR schem. Thus, it does not cover the unique roerties of n OR model such s different tyes of reltionshis including ggregtion. Regrding ssocition reltionshi, this work hs mentioned the usge of collection to store the reference. Nevertheless, it does not show the ste-by ste ming from concetul level down to the imlementtion. [7] rooses ming from the DTD into the OR Schem. The min contribution of the work is the usge of hybrid dtbse where the users cn select certin ttributes to be stored in ORDB nd others to be stored s they re (s XML dt). It does not show the ming for different kinds of reltionshi nd dt structures. [15] rooses the ming of the OO Concetul Model into the XML Schem. This work hs included collection for ggregtion reltionshi. However, the usge of UML for XML Dt is not comlete [3]. In ddition, this work does not discuss the usge of collection in ssocition reltionshi. XML DOCUMENTS AGGREGATION BOOK EDITION EDITION EDITION <xsd:element nme = BOOK tye = BookTye /> <xsd:comlextye nme = BookTye >... <xsd:element nme = EDITION minoccurs =?0? mxoccurs=?unbounded?/>... </xsd:element> PK book_id EN1 Book book_title Fundmentls of Dtbse System Book-Edition PK, FK PK book_id ed-no ed-yer EN EN EN XML DOCUMENTS ASSOCIATION CUSTOMER ORDER ORDER ORDER <xs:element nme = CUSTOMER tye = CustomerTye / > <xs:comlextye nme = CustomerTye > <xs:element nme = ORDER tye= OrderTye mx Occurs = unbounded />... </xs:comlextye> <xs:comlextye nme = OrderTye >... </xs:comlextye> Customer PK CustomerID CustomerNme MR2 Mrk Roberts Order PK PK FK OrderNo OrderDte CustomerID 1 25/08/2003 MR2 2 26/08/2003 MR2 3 27/08/2003 MR2 Figure. 2. Collection Flttened in Existing Method 704

3 Finlly [12, 13] roose the ming of ssocition nd ggregtion reltionshi of XML Schem to ORDB. In [12], the collection in XML Schem is disered in the tbles since they store the reference in the mny side or in the serte tble. In [13], the collection is reserved in the XML Schem, but gin the dt is stored sertely in cluster tbles or nested tbles. We find tht the existing works either hve not reserved the collection or hve reserved one ming ste only. Therefore, in this work we re going to roose the comlete ming to reserve the collection in ggregtion nd ssocition reltionshis, from the concetul level to the imlementtion. 2.2 Semntic Network: An Overview In this er we use the Semntic Network Method [3] to model the concetul level of the XML Documents structures. The digrm cn be viewed s richer lterntive of W3C XML Dt Model [14]. The Semntic Network Method is divided into the semntic level nd the schem level. The former develos secific digrm from the XML document structures while the ltter ms the digrm into syntx nd structure formlism such s DTD nd XML Schem. The semntic network digrm is divided into four mjor comonents: nodes, directed edges, lbels, nd constrints. In Figure 3, there re 5 nodes: A, B, X, Y, nd Z. The first two re comlex nodes while the rest re bsic nodes. There re four directed edges reresenting the semntic reltionshis between the objects. We hve different lbels corresonding to ech edge. For exmle indictes in-roerty reltionshi nd reresents ggregtion reltionshi. Finlly, there re constrints dded in nodes or edges such s uniqueness, crdinlity, dhesion, ordering, etc. This digrm cn show the concetul design of the XML documents more comletely thn XML dt model or UML [2]. X {unique} A Y [0..n] Figure. 3. Semntic Network Digrm In the schem level the Semntic Network Method ms the four comonents of the digrm into XML Schem, which is minly concerned with element/ttribute declrtions nd simle/ comlex tye definitions [4]. In the next section we show how we extend the schem level ming to cture the collection semntic then we follow through to the imlementtion of the XML Schem in ORDB. 3. PROPOSED METHODS FOR AGGREGATION RELATIONSHIP In this section we roose the ming methods for ggregtion reltionshis in the XML Dt into the ORDB. The imlementtion will be different bsed on the ggregtion constrints. B Z In the first ste we m both the whole nd the rt comonents s comlex tyes. The loction of the comlex tyes will be determined by the ggregtion constrints. For the second ste, we directly m the whole comlex tye s the tble nd the rt comlex tyes s the collection tye ttributes. Until the time of writing, SQL4 [8, 9] hve stndrdized two collection tyes, rry nd multiset. An rry is dynmiclly sized ordered collection tht llows dulictes. A multiset or bg is n unordered collection tht llows dulictes. The collection itself cn be of simle dt tye (such s INTEGER), constructed dt tye (such s ROW), or user-defined tye. 3.1 Imlementtion of Shreble nd Existence-Indeendent Aggregtion In the first tye of ggregtion, the rt comonents re shreble nd their existence is indeendent from the whole comonent. Therefore, we enble ccess to the rt comonent without firstly ccessing the whole comonent. The ming rules re shown below. Rule 1: Ste 1: For two tyes nmely T 1 nd T 2 with elements/ttributes (A,B) nd (M,N) resectively, if T 1 cn be comosed by collection of shreble nd existence-indeendent T 2, imlement T 1 s comlex tye nd T 2 s nother comlex tye ccessed s n element in T 1 with mxoccurs constrint = unbound. Ste 2: For two comlex tyes nmely T 1 (A,B) nd T 2 (M,N), if T 1 cn be comosed by more thn one shreble nd existence-indeendent T 2, imlement T 2 s collection of UDT ttribute of tble T 1. Trnsformtion result is Tble n T 1 (A, B, UDT T 2 (M, N)) 0 El. A El. B El. M El. N TYPE T 1 [0..n] Ste 1 TABLE T 1 Att A Att B Coll.T 2 Vl A Vl B Att M Att N Vl M 1 Vl N 1 Vl M 2 Vl N 2 Generl Syntx CREATE TYPE <T 2 tye schem> (tt i dt_tye,..., dt_tye); tt i+m TYPE T 2 XML Schem Ste 2 CREATE TABLE <T 1 tble schem> (tt j dt_tye,..., tt j+n MULTISET ARRAY (<T 2 tye schem>)); Figure 4. Aggregtion Tye 1 Trnsformtion Exmle 1: Tye STAFF is the ggregtion of tye DEPENDENT (see Fig.5). The ltter tye cn still exist outside tye STAFF, robbly in 705

4 tye STUDENT, etc. The ggregtion tye will be med into collections of UDT in ORDB tble. Note tht the horizontl line determines the ordering semntic. StffId StffNme DeNme STAFF order [0..n] DEPENDENT Figure 5. STAFF Aggregtion Exmle DeAge Trnsformtion into XML Schem (Ste 1): <xsd:comlextye nme = DEPENDENT_Tye > <xsd:sequence> <xsd:element nme = DeNme tye = <xsd:element nme = DeAge tye = xsd:integer / > </xsd:sequence> <xsd:comlextye nme = STAFF_Tye > <xsd:ttribute nme = StffID tye = xsd:id use = required /> <xsd:element nme = StffNme tye = <xsd:element nme = DEPENDENT tye = xsd:dependent_tye mxoccurs= unbounded /> Trnsformtion into ORDB (Ste 2): CREATE TYPE DeendentTye (DeNme CHARACTER VARYING(40), DeAge INTEGER)/ CREATE TABLE Stff (StffID CHARACTER VARYING(5) CONSTRAINT StffID_k PRIMARY KEY, StffNme CHARACTER VARYING(40), Deendent MULTISET (DeendentTye)); The first contribution of our method is the trnsformtion of semntic network to XML Schem. We come u with XML Schem where both the whole nd the rt comonents re defined s comlex tyes. Inside the whole comlex tye, we will hve n element of the rt comlex tye. Hving done this, the rt tye cn ctully be used inside nother whole comlex tye (shreble). To reserve the collection, we use the XML Schem syntx mxoccurs= unbounded. <xsd:comlextye nme = PART_Tye >... The second contribution is the trnsformtion of the XML Schem to the ORDB in the form of UDT collection ttribute. The ming is strightforwrd. The rt comlex tye is med s UDT nd the whole comlex tye is med s tble with one collection ttribute formed by the rt tye. We use the SQL syntx TABLE( MULTISET<ARRAY[]> (UDT_TYPE)). 3.2 Imlementtion of Non-Shreble nd Existence-Deendent Aggregtion For the next ggregtion tye, the rt comonents re nonshreble nd their existence deends on the whole comonent. This tye is usully clled comosition. We need to exclusively define the rt comonent inside the whole comonent. Rule 2: Ste 1: For two tyes nmely T 1 nd T 2 with elements/ttributes (A,B) nd (M,N) resectively, if T 1 cn be comosed by collection of non-shreble nd existence-deendent T 2, imlement T 1 s comlex tye nd T 2 s n inner comlex tye with mxoccurs constrint = unbound. Ste 2: For two comlex tyes nmely T 1 (A,B) nd T 2 (M, N), if T 1 cn be comosed by collection of shreble nd existence-deendent T 2, imlement T 2 s collection of ROW ttribute of tble T 1. Trnsformtion result is Tble n T 1 (A, B, Row T 2 (M, N)) 0 El. A El. B El. M El. N TYPE T 1 TYPE T 2 [0..n] Ste 1 Ste 2 TABLE T 1 Att A Att B Coll.T 2 Vl A Vl B Att M Att N Vl M 1 Vl N 1 Vl M 2 Vl N 2 XML Schem Generl Syntx CREATE TABLE <T 1 tble schem> (tt i dt_tye,..., tt i+m MULTISET ARRAY ROW (tt (i+m)(j) dt_tye,...)); Figure 6. Aggregtion Tye 2 Trnsformtion Exmle 2: COURSE is the comosition of two multile tyes ASSIGNMENT nd EXAM (see Fig.7). The comosition tye will be med into collections of row ttribute in ORDB tble. <xsd:comlextye nme = WHOLE_Tye > <xsd:element nme = PART_Nme tye = xsd:part_tye mxoccurs= unbounded />

5 CourseID [1..n] COURSE [1..n] CourseNme <xsd:comlextye nme = WHOLE_Tye >... <xsd:element nme = PART_Nme mxoccurs= unbounded />> <xsd:comlextye>... AssignTitle ASSIGNMENT order AssignTye ExmDte EXAM order Figure 7. COURSE Comosition Exmle ExmPercent Trnsformtion into XML Schem (Ste 1): <xsd:comlextye nme = COURSE_Tye > <xsd:ttribute nme = CourseID tye = xsd:id use = required /> <xsd:element nme = CourseNme tye = <xsd:element nme = ASSIGNMENT tye = mxoccurs= unbounded /> <xsd:comlextye> <xsd:sequence> <xsd:element nme = AssignTitle tye = <xsd:element nme = AssignTye tye = xsd:string /> </xsd:sequence> <xsd:element nme = EXAM mxoccurs= unbounded /> <xsd:comlextye> <xsd:sequence> <xsd:element nme = ExmDte tye = xsd:dte/> <xsd:element nme = ExmPercent tye = xsd:integer / > </xsd:sequence> Trnsformtion into ORDB (Ste 2): CREATE TABLE Course (CourseID CHARACTER VARYING(5) CONSTRAINT CourseID_k PRIMARY KEY, CourseNme CHARACTER VARYING(40), Assignment MULTISET (ROW (AssignTitle CHARACTER VARYING(40), AssignTye CHARACTER VARYING (20))), Exm MULTISET (ROW (ExmDte DATE, ExmPercent INTEGER))); In the second ste, we m the outer comlex tye s the tble in the ORDB nd the inner comlex tye s the ROW ttribute. To reserve the collection we imlement the ROW s collection with this syntx TABLE( MULTISET<ARRAY[]>(ROW()). 4. PROPOSED METHODS FOR ASSOCIATION RELATIONSHIPS In this section we roose the ming methods of the ssocition reltionshi in the XML structures into the ORDB using the collection tyes. As we wnt to ccommodte the collection, we only cover the ssocition with mny crdinlity: 1:N nd N:N. Like the revious section, the roosed method is divided into two stes. In the first ste we m the concetul model in the semntic network into the XML Schem. The ssociting tyes will become the comlex tyes. In the second ste we m the comlex tyes s the tbles nd the referentil object s the collection tye ttribute. 4.1 Imlementtion of 1:N Assocition For the 1:N ssocition reltionshi, the reference cn be stored s collection inside the tye tht hs one side. In usul rctice, the XML Schem ming to ORDB is not strightforwrd becuse the loction of reference key in both schems is different. Our method rooses more strightforwrd ming since the reference tye is lwys locted in the tye tht hs one side. Rule 3: Ste 1: For two tyes nmely T 1 (A,B) nd T 2 (M,N), if T 1 nd T 2 hs 1:N ssocition reltionshi, imlement both s comlex tyes with T 1 hs collection of reference to T 2 Ste 2: For two comlex tyes nmely T 1 (A,B) nd T 2 (M,N), if T 1 holds collection of reference to T 2, imlement both s tbles with T 1 hs collection ttribute refer to T 2. n Trnsformtion result is Tble T 1 (A, B, 2 _ Key ) nd Tble T 2 (M, N) T 1 The roosed method from the concetul to the imlementtion level hs ctured the rel semntic of the comosition hierrchy. In the first trnsformtion, we come u with the XML Schem where the rt comonent is defined s comlex tye inside the whole tye element. By doing this we void other element tye to shre the rticulr rt comonent (non-shreble constrint). We lso ensure tht on removl of the whole tye, we remove ll rt comonents tht re defined inside it (existence-deendent constrint). To reserve the collection, we use the XML Schem syntx mxoccurs= unbounded. 707

6 El. A El. B El. M El. N TYPE T1 TYPE T2 Ste 1 Ste 2 XML Schem Trnsformtion into ORDB (Ste 2): CREATE TABLE Building (BuildingID CHARACTER VARYING(5) CONSTRAINT BuildingID_k PRIMARY KEY, BuildingNme CHARACTER VARYING(40)); TABLE T 1 Att A Att B Coll.T 2 Vl A Vl B Vl M1 Vl M2 TABLE T 2 Att M Att N Vl M 1 Vl N 1 Vl M 2 Vl N 2 CREATE TABLE Fculty (FcultyID CHARACTER VARYING(5) CONSTRAINT FcultyID_k PRIMARY KEY, FcultyNme CHARACTER VARYING(50), BuildingID MULTISET(CHARACTER VARYING(5))); Generl Syntx CREATE TABLE <T 2 tble schem> (tt i dt_tye,..., tt i+m dt_tye); CREATE TABLE <T 1 tble schem> (tt j dt_tye,..., tt j+n MULTISET ARRAY (T 2 Key dt_tye)); Figure 8. 1:N Assocition Trnsformtion Exmle 3: Tye FACULTY hs n ssocition reltionshi with tye BUILDING (see Fig.9). The reference element/ttribute from one to mny side tye will be med s collections ttribute in ORDB tble. FcultyID FACULTY FcultyNme BUILDING BuildingNme BuildingID Figure 9. FACULTY-BUILDING Assocition Exmle Trnsformtion into XML Schem (Ste 1): <xsd:comlextye nme = BUILDING_Tye > <xsd:ttribute nme = BuildingID tye = xsd:id use = required /> <xsd:element nme = BuildingNme tye = <xsd:comlextye nme = FACULTY_Tye > <xsd:ttribute nme = FcultyID tye = xsd:id use = required /> <xsd:element nme = FcultyNme tye = <xsd:ttribute nme = BuildingID tye = xsd:string mxoccurs= unbounded /> <keyref nme= BUILDING_BuildingID_Ref refer= BUILDING_BuildingID > <selector xth = FACULTY > <field /></keyref> <key nme= FACULTY_FcultyID > <selector xth = FACULTY > <field /></key> In our method, we utilize the collection to store the reltionshi between two tyes. For the first trnsformtion we come u with two comlex tyes. In the one comlex tye we will hve collection of element of the mny comlex tye. To reserve the collection, we use XML Schem syntx mxoccurs= unbounded. And to mintin the reltionshi, we use key nd keyref insted of ID nd IDREF. Using the formers we enble one to secify scoe within which uniqueness lies. <xsd:comlextye nme = ONE_Tye >... <xsd:comlextye nme = MANY_Tye > <xsd:ttribute nme = ONE_Key... mxoccurs= unbounded />... <key nme= ONE_Key > <selector xth = ONE_Tye >...</key> <keyref nme= ONE_Key_Ref refer= ONE_Key > <selector xth = MANY_Tye >...</keyref> In the second ste, we m the comlex tyes s the tbles in the ORDB. In the mny tye we hve collection ttribute consist of ttribute key from the one tye. If we hve single key we will use collection of simle dt tye. Otherwise, we will hve collection of ROW tye. To reserve the collection the imlementtion syntx is TABLE( MULTISET<ARRAY[]> (SIMPLE_TYPE ROW()). We hve one shortcoming of using collection in the second ste of ssocition reltionshi. At resent, we cnnot use current SQL to embed integrity constrint checking in ORDB. As we know, in trditionl methods we cn include the foreign key or REF nd then define the integrity constrint checking such s ON DELETE CASCADE, ON UPDATE NULLIFY, etc. We still cnnot ly this for collection ttribute. Nevertheless, it does not men we cnnot hve integrity constrint checking for our methods. Triggers nd embedded routines re vilble in ORDB to enforce this tsk. 4.2 Imlementtion of N:N Assocition In the N:N ssocition, the reference cn be stored s collection inside one of the ssocited tye (see Fig.10). Our method rooses different wy of imlementing N:N ssocition becuse we do not require to store the reltionshi in serte tble. Rule 4: Ste 1: For two tyes T 1 (A,B) nd T 2 (M,N) hve N:N ssocition reltionshi in T 3 (X), imlement both s 708

7 comlex tyes with T 1 hs collection of T 3 nd reference to T 2. Ste 2: For two comlex tyes nmely T 1 (A,B) nd T 2 (M,N) hve N:N reltionshi, if T 1 hs the collection of the reltionshi nd the reference to T 2, imlement both s tbles with T 1 hs collection ROW ttribute. n Trnsformtion results re Tble T 1 (A, B, Row (T 2 Key, 1 T 3(X))) nd Tble T 2 (M, N) El. M El. N El. A El. B El. X TABLE T 2 Att M Att N Vl M 1 Vl N 1 Vl M 2 Vl N 2 TYPE T 2 TYPE T 1 TYPE T 3 Ste 1 Ste 2 XML Schem TABLE T 1 Att A Att B Coll. T 2 Key nd T 3 Vl A Vl B T2 Key T3 Att X Vl M 1 Vl X 1 Vl M 2 Vl X 2 Generl Syntx CREATE TABLE <T 2 tble schem> (tt i dt_tye,..., tt i+m dt_tye); CREATE TABLE <T 1 tble schem> (tt j dt_tye,..., tt j+n MULTISET ARRAY ROW (tt i dt tye,..., tt h dt tye,..., tt h+1 dt tye); Figure 10. N:N Assocition Trnsformtion Exmle 4: STUDENT nd SUBJECT hve N:N ssocition reltionshi (see Fig.11). The reference of one tye together with the reltionshis ttributes will be med s collection in nother tye tble. StudentID StudentNme STUDENT SubjectNme ENROLMENT SUBJECT Mrks SubjectCode Figure 11. STUDENT-SUBJECT Assocition Exmle Trnsformtion into XML Schem (Ste 1): <xsd:comlextye nme = SUBJECT_Tye > <xsd:ttribute nme = SubjectCode tye = xsd:id use = required /> <xsd:element nme = SubjectNme tye = <xsd:comlextye nme = STUDENT_Tye > <xsd:ttribute nme = StudentID tye = xsd:id use = required /> <xsd:element nme = StudentNme tye = <xsd:element nme = ENROLMENT_Tye mxoccurs= unbounded /> <xsd:comlextye> <xsd:sequence> <xsd:ttribute nme = SubjectCode tye = <xsd:element nme = Mrks tye = xsd:integer/> </xsd:sequence> <keyref nme= SUBJECT_SubjectCode_Ref refer= SUBJECT_SubjectCode > <selector xth = STUDENT/ENROLMENT > <field /></keyref> <key nme= STUDENT_StudentID > <selector xth = STUDENT > <field /></key> Trnsformtion into ORDB (Ste 2): CREATE TABLE Subject (SubjectCode CHARACTER VARYING(5) CONSTRAINT SubjectCode_k PRIMARY KEY, SubjectNme CHARACTER VARYING(20)); CREATE TABLE Student (StudentID CHARACTER VARYING(5) CONSTRAINT StudentID_k PRIMARY KEY, StudentNme CHARACTER VARYING(20), SubjectTken MULTISET (ROW (SubjectCode CHARACTER VARYING(5), Mrks NUMBER(3))); In the first ste we m the ssocited tyes into two serte comlex tyes. In one of the comlex tye we include the key to the other comlex tye s well s the reltionshi elements/ ttributes. Sme s 1:N ssocition, we use mxoccurs= unbounded with key nd keyref to reserve the collection nd the referentil constrint. The difference is now we hve dditionl elements/ttributes tht come u with the reltionshi. In the second ste we will likely to hve collection of ROW ttribute inside one of the mny side tble. It is becuse we need to include the key to the other mny side tble nd the dditionl reltionshi ttributes. To reserve the collection we imlement the collection with this syntx TABLE( MULTISET <ARRAY[]> (ROW()). 5. CONCLUSION By nture, the XML documents contin lot of collection structures. Mny works hve shred the sme solution in imlementing the collection in dtbse storge by ming them into flt tbles. This rctice hs diminished the concetul model semntic. With the existence of collection tyes in ORDB, we im to roose different imlementtion of collection structure in XML. In this er we show how the collection in the ggregtion nd the ssocition reltionshi of XML dt using semntic-network bsed concetul model cn be reserved in the imlementtion using the Object Reltionl Dtbse (ORDB). We roose the 709

8 usge of collection tye both for ggregtion nd ssocition reltionshi. In the ggregtion we differentite the method bsed on the hierrchy constrints, while in the ssocition we differentite bsed on the crdinlity. Unlike other works in trnsformtion, our roosed methods cover two strightforwrd ming stes, snned from the concetul model to the imlementtion into tbles. By doing this, the results mintin the semntic stted in the concetul level. In ddition, using collection tye, we hve utilized the rich fcility in ORDB. 6. REFERENCES [1] Bourret,R. Ming DTDs to Dtbses, in htt:// [2] Conrd, S., Scheffner, D. nd Freytg, J. XML Concetul Modeling using UML, ER 2000, Sringer-Verlg, 2000, [3] Feng, L., Chng, E. nd T. Dillon, A Semntic Network- Bsed Design Methodology for XML Documents, ACM TOIS 20(4), 2002, [4] Florescu, D. nd Kossmnn, D. Storing nd Querying XML Dt using n RDMBS, IEEE Dt Engineering Bulletin 22(3), 1999, [5] Fortier, P. SQL3 Imlementing the SQL Foundtion Stndrd, McGrw Hill, 1999 [6] Hn, W-S., Lee, K-H. nd Lee, B.S. An XML Storge System for Object-Oriented/Object-Reltionl DBMSs, Journl of Object Technology 2(1), 2003, [7] Klettke, M. nd Meyer, H. XML nd Object-Reltionl Dtbse Systems - Enhncing Structurl Mings Bsed on Sttistics, WebDB 2000, Sringer-Verlg, 2000, [8] Melton, J. (ed.), Dtbse Lnguge SQL Prt 2 Foundtion. ISO-ANSI WD , Interntionl Orgniztion for Stndrdiztion, Working Grou WG3 (August 2002) [9] Prdede, E., Rhyu, J.W. nd Tnir, D. New SQL Stndrd for Object-Reltionl Dtbse Alictions, SIIT 2003, Delft TU, 2003, [10] Rumbugh, J. et l, Object-Oriented Modelling nd Design, Prentice Hll, 1991 [11] Shnmugsundrm, J., Tufte, K., Zhng, C. He, Ge. DeWitt, D.J. nd Nughton, J.F. Reltionl Dtbses for Querying XML Documents: Limittions nd Oortunities, VLDB 1999, Morgn-Kuffmn, 1999, [12] Widjy, N.D., Tnir, D., Rhyu, J.W. nd Prdede, E. Assocition Reltionshi Trnsformtion of XML Schems to Object-Reltionl Dtbses, iiwas 2002, SCS Publishing House, 2002, [13] Widjy, N.D., Tnir, D. nd Rhyu, J.W. "Aggregtion Trnsformtion of XML Schems to Object-Reltionl Dtbses", IICS 2003, Sringer-Verlg, 2003 [14] W.W.W, The XML dt model, vilble t htt:// [15] Xiou, R., Dillon, T.S., Chng, E., nd, Feng, L. Modeling nd Trnsformtion of Object-Oriented Concetul Models into XML Schem, DEXA 2001, Sringer-Verlg, 2001,