Querying Moving Objects in SECONDO

Transcription

1 Querying Moving Objecs in SECONDO Vicor Teixeira de Almeida, Ralf Harmu Güing, and Thomas Behr LG Daenbanksyseme für neue Anwendungen Fachbereich Informaik, Fernuniversiä Hagen D Hagen, Germany {vicor.almeida, rhg, Absrac Represening descripions of movemens in daabases and querying hem is a basic capabiliy required in mobile daa managemen. In his demonsraion, we show for he firs ime a prooype implemening a daa model and query language for moving objecs (rajecories) compleely inegraed ino a DBMS environmen, including query opimizaion and user inerface issues such as animaion. 1. Inroducion Locaion aware mobile devices have become a cheap commodiy. For example, here are already millions of users of GPS-equipped PDAs or car navigaion sysems. Such sysems can also record movemens. RFID ags are used as well o rack he movemens of goods. Such rends will resul in he collecion of massive amouns of moving objec daa, someimes called rajecories, in he near fuure. There is a grea ineres in being able o represen such movemens in daabases in order o perform analysis on hem, daa mining, as well as ad-hoc querying. The research area of moving objecs daabases has addressed his need, and here has already been a lo of research in he las years ranging from daa models and query languages o implemenaion aspecs such as efficien index srucures (see [GS05]). A query language for moving objecs based on he idea of spaio-emporal absrac daa ypes has been developed in earlier work [GBE+00]. Implemenaion aspecs such as daa srucures for he ypes and algorihms for he operaions have also been addressed [FGNS00, CFG+03]. In his demonsraion we show for he firs ime a prooype of his design. An algebra for moving objecs has been implemened in he SECONDO exensible DBMS environmen. The design could be implemened in a similar way in oher objec-relaional or exensible sysems. SECONDO is a DBMS prooyping environmen paricularly geared for exension by algebra modules for nonsandard applicaions. I is complee in he sense ha all aspecs needed by such applicaions, ranging from efficien query processing in he sysem kernel hrough opimizaion o an exensible user inerface are addressed. Examples in his paper are based on he Berlin daabase. I conains various geographic daa ses from he ciy of Berlin. To his we have added a synheic daa se for moving objecs, namely a relaion describing underground rains as moving poins. The moving poin daa have been generaed by maching rain schedules o rain line geomeries. Whereas analyzing rain movemens is perhaps no he mos exciing applicaion, i is a scenario ha is easily undersood, and he query examples can easily be ranslaed o oher domains. Since we have he daa available, he queries in he paper can indeed be demonsraed. This demonsraion should be ineresing because: I is o our knowledge he firs presenaion of a sysem ha implemens a moving objecs daa model and query language compleely inegraed ino a DBMS environmen. All sysem levels including kernel, query opimizaion, and user inerface wih animaion for moving objecs are included and can be demonsraed. The SECONDO sysem has been demonsraed before, wih a focus on archiecure and exensibiliy and he use for prooyping and eaching [GAA+05]. This is he firs demo addressing moving objecs. The complee SECONDO sysem, including he moving objecs algebra demonsraed here, is freely available for download a hp:// 2. Algebra for Moving Objecs In his secion we review he sysem for represening moving objecs presened in [GBE+00, FGNS00]. The core of his sysem are he absracions moving poin and moving region, describing objecs wih ime-dependen posiion such as vehicles and mobile-phone users, and objecs where he shape and exen are also ime dependen, such as hurricanes and oil spills. These absrac daa ypes (and heir discree represenaions described in [FGNS00]) may be embedded as aribue ypes ino OO- or ORDBMS, or implemened as exension packages ino exensible DBMS. We use he laer approach wih he SECONDO Exensible DBMS [GBA+04], which is he subjec of he nex secion. Temporal ypes use he sliced represenaion, which represens a ime-dependen value as a sequence of slices (emporal unis) such ha wihin each slice, he developmen of he value can be represened by a simple func-

2 ion, he so-called emporal funcion. As an example, for values ha can only change discreely (e.g. in and bool) a consan funcion is applied. For he moving real (mreal), he funcion is a quadraic polynomial or square roo of such (Figure 1(a)). Poins move linearly inside each slice in he moving poin (mpoin) represenaion (Figure 1(b)). v Figure 1: Sliced represenaion of a moving real and a moving poin For moving regions (mregion), verices of regions also move linearly inside each slice, wih several resricions applied o ensure ha, for every ime insan inside he slice, a valid region is defined by he emporal funcion. More deails abou he represenaion of he moving objec daa ypes can be found in [FGNS00]. Figure 2 shows a sample slice of a moving region. (a) y x Figure 2: Sample slice of a moving region Over hese daa ypes, a large se of operaions is defined in [GBE+00]. Firs, generic operaions on nonemporal daa ypes are provided including predicaes, se operaions, aggregae operaions, ec. Examples are: poin region bool inside region region region union line real lengh poin poin real disance where inside checks wheher a poin is inside a region, union reurns he region which is he union of he wo argumen regions, lengh reurns he oal lengh of a line, and disance compues he (Euclidean) disance beween wo poins. Then, by an approach called lifing, all operaions defined in his firs sep are available for he corresponding emporal ypes. For example, he inside operaor can be applied in he following ways mpoin region mbool inside poin mregion mbool mpoin mregion mbool where he argumens as well as he reurn value are lifed o heir emporal counerpars. Finally, special operaors for emporal ypes are offered wih projecions ino ime and range of values, inersecions wih values or ses of values from ime and range of values, and resuls ha deermine rae of change. Examples of such operaors (appearing in queries below) are: mpoin line rajecory mpoin periods mpoin aperiods mpoin periods bool presen mpoin insan bool presen mpoin periods defime y (b) x mpoin region mpoin a mpoin region bool passes mpoin poin bool passes mpoin insan ipoin ainsan ipoin insan ins ipoin poin val Here rajecory projecs he moving poin o he 2-d plane as a line value; aperiods resrics he movemen o some period of ime; presen checks wheher he moving objec exiss a a predefined period or insan of ime; and defime projecs he movemen o he ime dimension. Operaion a resrics a moving poin o he imes when i is inside a region, passes checks wheher i is ever inside a region or a a poin. Finally, ainsan evaluaes he moving poin a given insan of ime, reurning a pair consising of he insan and a poin, a value of ype ipoin, for which ins and val reurn he componens. Now we are able o show how he absrac daa ypes can be embedded ino a (relaional) DBMS daa model and how he available operaions can be used in queries. Assume ha we have he following relaions conaining a se of underground rains and he rain saions in Berlin. There are 562 rains and 173 saions. Each rain conains abou 100 emporal unis. A larger version of his daabase is described in Secion 4. Trains(Id:in, Line:in, Up:bool, Trip:mpoin) Saions(SName:sring, Type:sring, Loc:poin) A rain sysem adminisraor could ask Where exacly were he rains beween 8:00 and 8:01 o clock? : SELECT Id, Line, rajecory(trip aperiods eigh00) AS Srech FROM Trains WHERE Trip presen eigh00; where eigh00 is he period from 8:00 unil 8:01 o clock. A wha imes have rains passed hrough (underground) he park Tiergaren? SELECT FROM WHERE Id, Line, defime(trip a iergaren) AS Times Trains Trip passes iergaren; Here iergaren is a region value for he park area. The following query will be used hroughou he res of he paper: Where have he rains passing hrough he Mehringdamm saion been a 6:50 am (as far as hey are moving a his ime): SELECT Id, Line, val(trip ainsan sixfify) AS Pos FROM Trains, Saions WHERE Trip passes Loc AND SName conains Mehringdamm AND Trip presen sixfify Here sixfify is a value of ype insan. 3. Moving Objecs Algebra in SECONDO In his secion we presen implemenaion issues of he moving objec algebra in SECONDO, emphasizing he changes needed in order o accommodae he new daa ypes and operaions. The goal of SECONDO is o provide a generic daabase

3 sysem frame ha can be filled wih implemenaions of various DBMS daa models. For example, i should be possible o implemen relaional, objec-oriened, emporal, or XML models and o accomodae daa ypes for spaial daa, moving objecs, chemical formulas, ec. In his paper we deal wih he relaional daa model wih exensibiliy capabiliies o provide he daa ypes as aribues for moving objecs. The SECONDO sysem consiss of hree major componens shown in Figure 3: Figure 3: SECONDO Componens. The SECONDO kernel implemens specific daa models, is exensible by algebra modules, and provides query processing over he implemened algebras. I is wrien in C++. The opimizer provides as is core capabiliy conjuncive query opimizaion, currenly for a relaional environmen, and also implemens he essenial par of SQL-like languages. I is wrien in PROLOG. The graphical user inerface (GUI) is an exensible inerface for an exensible DBMS such as SECONDO, where new daa ypes or models can provide heir own viewers or exend an exising viewer by display mehods. I is wrien in Java The Kernel Alg 1 GUI Opimizer SECONDO Kernel Command Manager Query Processor & Caalog... Alg n Spaial Temporal Sorage Manager & Tools A very rough descripion of he archiecure of he SEC- ONDO kernel is shown in Figure 4. A daa model is imple- Figure 4: Rough archiecure of he kernel mened as a se of daa ypes and operaions. These are grouped ino algebras. For example, here is an algebra wih relaions and uples as daa ypes and operaions like projecion or hashjoin. Index srucures are also offered as algebras; currenly SECONDO has an algebra for B-rees and anoher one for R-rees. The focus of his paper is in he implemenaion of he Spaial and he Temporal Algebras. The Spaial Algebra implemens he ypes poin, poins, line, and region following he implemenaion of he ROSE Algebra ([GRS95]). The Temporal Algebra mainly provides ypes for moving poins and moving regions following he descripion in [FGNS00]. For every moving daa ype, a uni daa ype is provided implemening he corresponding emporal funcion, e.g. for he mpoin daa ype, he upoin is also provided. A subse conaining he mos imporan operaors in [GBE+00] is implemened. The kernel can evaluae a query plan, also called an execuable query, or a query a he execuable level, which is jus a erm of he implemened algebras. Query processing is performed as follows: he Command Manager receives an execuable query, parses i and passes he resul o he Query Processor. The Query Processor hen evaluaes he query by building an operaor ree and hen raversing i, calling operaor implemenaions from he algebras. More deails abou his process can be found in [DG00]. SEC- ONDO objecs are sored (and rerieved) by he Sorage Manager ino a daabase and managed by he Caalog. As an example, one possible way of wriing he las query of Secion 2 a he execuable level is: Trains feed filer[.trip presen sixfify] Saions feed filer[.sname conains "Mehringdamm"] symmjoin[.trip passes..loc] exend[pos: val(.trip ainsan sixfify)] projec[id, Line, Pos] consume where feed, filer, symmjoin, exend, projec, and consume are operaors of he Relaional Algebra. Feed convers a relaion ino a sream of uples and consume does he conrary, filer filers he sream of uples given a condiion, exend adds a calculaed aribue o he uple, and projec projecs he uples o he given aribues. The do is used o rerieve an aribue from he given uple. Symmjoin is a symmeric varian of nesed loop join, he double do noaion refers o an aribue of a uple of he second argumen The Opimizer The opimizer provides as is core funcionaliy cos-based opimizaion of conjuncive queries. Tha is, i receives a se of relaions ogeher wih a collecion of selecion and join predicaes, and produces a plan. I employs a novel algorihm for query opimizaion described in deail in [GBA+04], based on shores pah search hrough a predicae order graph. This echnique is remarkably simple o implemen, ye is efficien and is guaraneed o find he opimal plan even in he presence of expensive predicaes 1. The opimizer is wrien in PROLOG, using he SWI- PROLOG sysem. PROLOG is an excellen language for implemening opimizers, exensible opimizers in paricular as new opimizaion rules can be formulaed easily. I is also very efficien for his kind of ask. The SECONDO opimizer handles queries wih up o en predicaes in less han a second. The number of relaions involved plays no role. On op of he conjuncive query opimizer, he essenial pars of an SQL-like language have been implemened. The SQL noaion was slighly adaped so ha queries can be wrien direcly as PROLOG erms. The algebra for moving objecs, like oher non-sandard applicaions, poses he following requiremens o an opi- 1. This is, of course, relaive o he given cos funcions, assuming correc esimaions of seleciviy and no correlaions.

4 op-server > opimizaion-inpu : selec [id, line, val(rip ainsan sixfify) as pos] from [rains, saions] where [rip passes loc, sname conains "Mehringdamm", rip presen sixfify] Compuing bes Plan... Elapsed Time: 1218 ms Predicae Cos: ms Seleciviy : Elapsed Time: 62 ms Predicae Cos: ms Seleciviy : Desinaion node 7 reached a ieraion 5 Heigh of search ree for boundary is 2 opimizaion-resul : Trains feed projec[id, Line, Trip] Saions feed projec[loc, SName] filer[(.sname conains "Mehringdamm")] symmjoin[(.trip passes..loc)] filer[(.trip presen sixfify)] exend[pos: val((.trip ainsan sixfify))] projec[id, Line, Pos] consume op-server > Figure 5: Proocol of he SECONDO opimizer mizer: Seleciviy esimaion mus work for complex daa ypes and an exremely large se of operaions. The radiional hisogram-based approach does no scale o his case. Operaions can be expensive; hence expensive predicaes mus be suppored in opimizaion. SECONDO provides seleciviy esimaion by sampling; for each relaion a small maerialized sample is kep. Unknown seleciviies are deermined in advance by sending seleciviy queries o he kernel before saring he proper opimizaion process; hey are hen sored for laer use. The cos for expensive predicaes is deermined as well in he execuion of he seleciviy queries on samples by measuring he acual execuion ime, subracing overhead. The beauy of his scheme is ha opimizaion works o a large exen auomaically wihou manual work when a new algebra wih non-sandard ypes is added. Wha has o be provided manually are opimizaion rules for adding specialized indexes, and possibly synax rules for operaions (he laer is very easy). An example ineracion wih he SECONDO opimizer is shown in Figure 5. I shows he example query from Secion 2 as wrien by he user. Here all symbols are wrien in lower case, and he PROLOG noaion for liss is used. For he wo predicaes rip passes loc and sname conains Mehringdamm, seleciviies and predicae evaluaion coss are deermined (for rip presen sixfify his was known already). Then he query plan is consruced and shown. The laer is a erm of he execuable level of SECONDO ha is readable and which can as well be yped in direcly, e.g. for experimening The User Inerface A visualizaion of query resuls is possible in he graphical user inerface Javagui of he SECONDO sysem. Javagui communicaes wih he sysem kernel and he opimizer via TCP/IP. I can be exended by viewers. Each viewer can display a se of differen daa ypes. In his way, Javagui is able o display each ype implemened in he sysem kernel. The user inerface consiss of hree pars (see Figure 7), namely he command area (op-lef), he objec manager (op-righ), and an area conaining he curren viewer (boom). In he command area, he user can inpu queries and commands conrolling Javagui. Javagui recognizes wheher a query is given a he execuable level or in he synax of he opimizer. If he query is in opimizer synax, Javagui sends i o he opimizer and receives a plan a he execuable level. This plan is sen o he sysem kernel. The resul of a query is delivered in a generic forma based on nesed lis srucures o he objec-manager. I sores he resul of he query, selecs a viewer able for displaying he resul, and finally i ransfers he query resul o his viewer for furher processing. The HoeseViewer (named by is auhor) is a fairly sophisicaed viewer for spaial and spaio-emporal daa. This viewer can be exended for displaying furher daa ypes using display classes. Exising implemenaions include classes for displaying: simple ypes like ineger and sring spaial ypes like poin, line, and region emporal ypes, e.g. moving reals spaio-emporal ypes, for example, moving poins and moving regions The HoeseViewer conains in principle hree areas displaying differen informaions abou query resuls. A he lef, exual informaion is shown. The righ par is divided ino a big area displaying spaial and spaio-emporal objecs and a smaller area for emporal daa, e.g. periods or moving reals (his area is no shown in Figure 7). Depending on he ype o display, each display class convers an objec given as a nesed lis ino an inernal forma, e.g. a sring or a geomerical objec. For spaioemporal objecs, a display class has o provide a mehod aking an insan and reurning he shape of his objec a his insan or nohing when he objec is no defined a his ime. If an objec does no fi well ino exising areas, he class implemener is free o creae a new window. This is done for example wihin display classes for ex, picures and moving reals. For spaial and spaio-emporal objecs, he appearance (linewidh, filling ec.) can be changed o he user s preferences. This and furher funcionaliy like zooming and labeling of objecs are par of he HoeseViewer. A display class mus no worry abou such hings. Moving spaial objecs are animaed. The animaion is conrolled using a few buons and a slider (Figure 6). Figure 6: Conrolling he animaion Using he ime slider, any insan can be seleced. The ani-

5 his demonsraion will be o show he animaion of moving objecs in he user inerface of SECONDO. Moving Region Daa. This small sample daabase conains some regions, moving poins, and moving regions. We will show wih his example query processing using he moving region daa ype. Big Berlin Daabase. We ranslaed he Berlin daabase five imes in all direcions: x, y, and ime. We hen have a daabase ha is 125 imes larger han he Berlin daabase. Wih his daabase we can show how queries scale wih bigger daa ses and how indexes are used. Acknowledgemens maion speed can be doubled or halved by he corresponding buons. By he remaining buons, he animaion can be sared/sopped or se o is begin or o is end. Below he ime slider, he curren ime of he animaion and he spaial posiion of he cursor can be seen. If an objec is seleced, he objec is kep in he visible area of he animaion. For seeing moving objecs wihin a spaial conex, a picure, e.g. a ciy map, can be used as background image. Non-spaial emporal objecs can be shown a he boom righ or in a new window. The defaul is he display of he single unis wihin he HoeseViewer. For moving real values an implemenaion exiss opening a new window showing he value of his objec as a funcion of ime. 4. Wha Will be Demonsraed Figure 7: The graphical user inerface The demonsraion will be focused on query execuion and visualizaion, and will be divided ino pars, using he following daabases. The Berlin Daabase. The Berlin daabase conains several relaions wih spaial objecs such as srees, underground rain lines, green and waer areas, sighseeing spos, resaurans, ec. and a relaion conaining several lines of underground rains as moving poins. We will show he capabiliies of all hree componens of SECONDO performing several differen queries in his daabase. GPS Daa. This daabase conains some real daa abou racings colleced using a GPS device. The main focus on References We hank Slaven Rezic for allowing us o use he Berlin daabase aken from he BBBike applicaion (hp:// bbbike.sourceforge.ne). We also hank everybody ha has conribued in he developmen of SECONDO and he algebra for moving objecs, especially Markus Spiekermann, Zhiming Ding, Frank Hoffmann, Thomas Höse, and Holger Münx. [CFG+03] J. A. Coelo Lema, L. Forlizzi, R. H. Güing, E. Nardelli, M. Schneider, Algorihms for Moving Objecs Daabases, The Compuer Journal, 46(6), [DG00] S. Dieker and R.H. Güing, Plug and Play wih Query Algebras: SECONDO. A Generic DBMS Developmen Environmen. Proc. IDEAS 2000, [FGNS00] L. Forlizzi, R.H. Güing, E. Nardelli, and M. Schneider, A Daa Model and Daa Srucures for Moving Objecs Daabases. In Proc. ACM SIGMOD Inl. Conf. on Managemen of Daa, 2000, [GAA+05]R.H. Güing, V.T. de Almeida, D. Ansorge, T. Behr, Z. Ding, F. Hoffmann, M. Spiekermann, and U. Telle, SEC- ONDO: An Exensible DBMS Plaform for Research Prooyping and Teaching. In Proc. 21s Inl. Conf. on Daa Engineering (ICDE), 2005, [GBA+04]R.H. Güing, T. Behr, V.T. de Almeida, Z. Ding, F. Hoffmann, and M. Spiekermann, SECONDO: An Exensible DBMS Archiecure and Prooype. Fernuniversiä Hagen, Informaik-Repor 313, [GBE+00] R.H. Güing, M.H. Böhlen, M. Erwig, C.S. Jensen, N.A. Lorenzos, M. Schneider, and M. Vazirgiannis, A Foundaion for Represening and Querying Moving Objecs. ACM Transacions on Daabase Sysems, 25(1): 1-42, [GRS95] R.H. Güing, T. de Ridder, and M. Schneider, Implemenaion of he ROSE Algebra: Efficien Algorihms for Realm-Based Spaial Daa Types. In Proc. 4h. Inl. Symp. on Advances in Spaial Daabases (SSD), 1995, [GS05] R.H. Güing and M. Schneider, Moving Objecs Daabases. Morgan Kaufmann Publishers, 2005.