We present the WebdamLog system for managing distributed data on the Web in a
peer-to-peer manner. We demonstrate the main features of the system through an
application called Wepic for sharing pictures between attendees of the sigmod
conference. Using Wepic, the attendees will be able to share, download, rate
and annotate pictures in a highly decentralized manner. We show how WebdamLog
handles heterogeneity of the devices and services used to share data in such a
Web setting. We exhibit the simple rules that define the Wepic application and
show how to easily modify the Wepic application.Comment: SIGMOD - Special Interest Group on Management Of Data (2013

Abiteboul, Serge

Antoine, Émilien

Miklau, Gerome

Stoyanovich, Julia

Testard, Jules

English

arXiv

Serge Abiteboul

Émilien Antoine

Gerome Miklau

Julia Stoyanovich

Jules Testard

Crossref

Rule-based application development using Webdamlog

International audienceWe present the WebdamLog system for managing distributed data on the Web in a peer-to-peer manner. We demonstrate the main features of the system through an application called Wepic for sharing pictures between attendees of the sigmod conference. Using Wepic, the attendees will be able to share, download, rate and annotate pictures in a highly decentralized manner. We show how WebdamLog handles heterogeneity of the devices and services used to share data in such a Web setting. We exhibit the simple rules that define the Wepic application and show how to easily modify the Wepic application

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HAL Id: hal-00817791https://hal.inria.fr/hal-00817791Submitted on 14 May 2013HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestinée au dépôt et à la diffusion de documentsscientifiques de niveau recherche, publiés ou non,émanant des établissements d’enseignement et derecherche français ou étrangers, des laboratoirespublics ou privés.Rule-Based Application Development using WebdamlogSerge Abiteboul, Émilien Antoine, Gerome Miklau, Julia Stoyanovich, JulesTestardTo cite this version:Serge Abiteboul, Émilien Antoine, Gerome Miklau, Julia Stoyanovich, Jules Testard. Rule-BasedApplication Development using Webdamlog. SIGMOD - Special Interest Group on Management OfData, 2013, New York, United States. ￿hal-00817791￿Rule-Based Application Development using Webdamlog ∗Serge AbiteboulInria Saclay & ENS Cachanfirst.last@inria.frÉmilien AntoineInria Saclay & ENS Cachanfirst.last@inria.frGerome MiklauInria Saclay & UMass Amherstmiklau@cs.umass.eduJulia StoyanovichDrexel University & Skoltechstoyanovich@drexel.eduJules TestardInria Saclay & McGill U.Jules.Testard@mail.mcgill.caMay 14, 2013We present the WebdamLog system for managing distributeddata on the Web in a peer-to-peer manner. We demonstratethe main features of the system through an application calledWepic for sharing pictures between attendees of the sigmodconference. Using Wepic, the attendees will be able to share,download, rate and annotate pictures in a highly decentralizedmanner. We show how WebdamLog handles heterogeneity ofthe devices and services used to share data in such a Web set-ting. We exhibit the simple rules that define the Wepic appli-cation and show how to easily modify the Wepic application.1 IntroductionInformation management on the Internet relies on a wide vari-ety of systems, each specialized for a particular task. A user’sdata and favorite applications are often distributed, making themanagement of personal data and knowledge (i.e., programs)a major challenge. Consider Joe, a typical Web user who hasa blog on Wordpress.com, a Facebook account, a Dropbox ac-count, and also stores data on his smartphone and laptop. Joeis a movie fan and he wants to post on his blog a review of thelast movie he watched. He also wishes to advertise his reviewto his Facebook friends and to include a link to his Dropboxfolder where the movie has been uploaded. This is a cumber-some task to carry out manually, yet automating it, for exampleby writing a script, is far beyond the skills of most Web users.Some systems attempt to provide integrated services to sup-port such needs. For instance, Facebook provides a wrapperservice to integrate Dropbox accounts and blogs. However,such services are often limited in the functionality they support.Also, by delegating such services to systems like Facebook, auser needs to trust more and more of his information to oneparticular system. Our goal is to enable the user to easily spec-ify distributed data management tasks in place (i.e., withoutcentralizing his data to a single provider), while allowing himto keep full control over his own data [4]. Our system is nota replacement for Facebook, or any centralized system, but itallows users to launch their customized peers on their machineswith their own personal data, and to collaborate using Webservices.This demonstration presents the Wepic application, a dis-tributed picture manager. The Wepic application is specifiedusing simple rules written in a declarative language called Web-damLog [2] and it runs on the WebdamLog system, demon-strated here for the first time. WebdamLog is a rule-based∗This work has been partially funded by the European ResearchCouncil under the European Community’s Seventh Framework Pro-gram (FP7/2007-2013); ERC grant Webdam, agreement 226513.http://webdam.inria.fr/datalog-style language that emphasizes cooperation betweenautonomous peers by allowing both data, and programs thatcompute on data, to be easily exchanged. The declarative ap-proach alleviates the conceptual complexity on the user while,at the same time, allowing for powerful performance optimiza-tions on the part of the system.A central issue in such a setting is the ease with which acasual user can write WebdamLog rules. We conducted a userstudy, showing that users are able to both understand and writesimple WebdamLog programs with a minimal amount of train-ing [5]. This demonstration further argues for the simplicity ofusing WebdamLog for designing applications that handle per-sonal data.sigmod attendees will use Wepic to share, download, rateand annotate pictures taken at the conference. Attendees willuse the application via a Web GUI or launch their own Wepicpeer. They will first inspect the basic WebdamLog rules of theprovided application and will then be invited to customize theapplication by modifying or adding rules.2 Language and SystemWebdamLog language, in brief WebdamLog extends datalogin a number of ways, supporting updates, distribution, nega-tion, and a novel feature called delegation.Facts. A fact is an expression of the form m@p(a1, ..., an),where a1, ..., an are data values and m@p is a relation describedby relation name m and peer name p. Variables start with thesymbol $, e.g. $x, and data values are quoted. An example ofa fact is:pictures@sigmod(32, “sea.jpg”, “Émilien”, 100. . . , . . .)where pictures@sigmod is a relation managed at the sigmodpeer to represent a collection of pictures. The picture name is“sea.jpg”, its content is in binary “100. . . ”, and the remainderof the fact consists of meta-data about the picture.Rules. A term is a constant or a variable. A rule in a peerp is an expression of the form:$R@$P($U) :- $R1@$P1($U1) , . . . , $Rn@$Pn($Un)where $R and $Ri are relation terms, $P and $Pi are peer terms,$U and $Ui are vectors of terms.Distribution/Delegation. WebdamLog supports distri-bution, allowing atoms in the body of a rule to refer to relationson remote peers (using variables denoting relations or peers).The evaluation of such a rule therefore requires the knowledgeand processing of possibly more than one peer. In addition,delegation allows a peer to install a rule at a remote peer, wherethe rule itself may refer to local or remote relations. Rule bod-ies in WebdamLog are evaluated from left to right. The ordermatters, unlike in datalog where the order of atoms in a rule1body is not relevant. Although negation is supported by thelanguage, it is not yet implemented in the WebdamLog system.WebdamLog peers, in brief Each peer runs a WebdamLogprogram, i.e., a set of rules, using a WebdamLog engine.The evaluation of datalog has been studied for decades buta renewed interest in datalog [1, 8, 9] has led to the recentdevelopment of the Bud [6] datalog engine, which we use aspart of our implementation. The Bud system supports effi-cient communication between peers and updates of base facts.A computation stage of the WebdamLog engine is brokendown into three steps. First, the peer loads the inputs re-ceived from the remote peers since the previous stage. Second,the peer runs a fixpoint computation of its program. Third,the peer sends facts (updates) and rules (delegations) to otherpeers. A main novelty is the possibility for WebdamLog rules tohave variables as relation and peer names. Another main nov-elty is delegation, which leads to installing, at run-time rules,at other peers. As a result, WebdamLog programs may be verydynamic, peers may discover new peers and new relations andthey may acquire new rules as the result of delegations.The WebdamLog system follows prior work on a P2P systemfor sharing data called WebdamExchange [3, 7]. The presentfocus is very different (declarative specification and delegationin WebdamLog vs. security in WebdamExchange), so little ofthe previous system could be re-used.Wrappers The WebdamLog system has been designed for in-tegration with the personal data of regular Web users who al-ready use popular Web systems such as Facebook, Picasa orDropbox. The WebdamLog system supports the managementof data in these systems by using wrappers. A wrapper tosome existing system X provides software that exports to Web-damLog one or more relations corresponding to the data in X,as well as rules to access/update this data.For example, in the demonstration we will use a Facebookwrapper. For a given Facebook user Émilien, our wrapper willsimulate a peer ÉmilienFB with two relations:friends@ÉmilienFB($userID, $friendName)pictures@ÉmilienFB($picID, $owner, $URL)These two relations provide an abstract view of Émilien’s Face-book data relevant to this particular application, and can thenbe used in WebdamLog rules.Access control Since many WebdamLog applications willmanage personal or social data, access to sensitive informationmust be carefully controlled. Access control in WebdamLogis particularly challenging because of the distributed nature ofcomputation and the ability of peers to delegate rules to otherpeers. We describe in the next section the features includedin the demonstration for controlling the delegation of rules, inwhich a peer is asked to explicitly accept delegations initiatedby other peers.A complete access control model for WebdamLog is under ac-tive investigation and is not included in the demonstration. Inthat model, access to stored or derived relations is controlled bya novel combination of both discretionary methods (in whichusers have the power to grant rights to data they own) andmandatory methods (in which access rights are derived accord-ing to system-wide conventions). Users directly specify the ac-cessibility of stored relations that they own. For derived rela-tions (i.e. views), a user may rely on a default access controlpolicy that is derived automatically from the provenance of thebase relations. Alternatively, a user may override this policy inorder to grant access to views, effectively “declassifying” somedata. This flexible model subsumes the view-based access con-trol of the standard SQL authorization model.3 The Wepic applicationTo demonstrate the WebdamLog system, we introduce an ap-plication called Wepic, a conference picture manager for thesigmod conference. This application allows conference atten-dees to share their pictures and to rate, annotate and downloadthe pictures of others.Wepic consists of a small set of rules that we discuss fur-ther. In addition, the application uses two standard wrapperswe implemented, one for Facebook, and one for email commu-nications. The WebdamLog system provides a graphical inter-face, which has been customized to provide a user interface forWepic. It is shown in Figure 1.A user connected to a Wepic peer can:1. Upload a picture from a file or a URL;2. View pictures provided by a particular attendee;3. Transfer pictures:a) send them by email to the sigmod group on Facebook,or to another Wepic peer,b) get pictures from another Wepic peer or from the sig-mod group on Facebook;4. Annotate pictures with ratings, comments or name tags(names of attendees appearing in the picture);5. Select and rank photos based on their annotations.Figure 1: A screenshot of the Wepic user interface.We now illustrate how some of these units of functionalityare implemented with WebdamLog rules. To view picturesuploaded by a particular sigmod attendee, we use a relationselectedAttendees that contains one fact for each currently high-lighted attendee (see right-hand side column in Figure 1). Wealso use a derived relation pictures, which is the view of all thepictures of a particular attendee. To obtain the pictures of allselected attendees, we use the rule:attendeePictures@Jules($id, $name, $owner, $data) :-selectedAttendee@Jules($attendee),pictures@$attendee($id, $name, $owner, $data)Note that this rule uses delegation, a feature novel to Web-damLog, to retrieve the contents of relation pictures of eachattendee. The result of executing this rule is shown in the At-tendee pictures frame at the bottom of Figure 1.2Figure 2: The distribution of peers in the network.To transfer pictures between peers, we assume that each at-tendee specifies some preferred communication protocols in re-lation communicate, stating, e.g., whether he prefers to receivepictures by email, by posting on Facebook, or directly in hisWepic peer. The following rule is executed when Jules sendssome pictures to some attendees:$protocol@$attendee($attendee, $name, $id, $owner) :-selectedAttendee@Jules($attendee),communicate@$attendee($protocol),selectedPictures@Jules($name, $id, $owner)Rules of this kind, and other rules implementing the basicfunctionality of Wepic, are available for inspection and cus-tomization through the user interface, see Figure 3.Delegation and access control As noted in Section 2, by usingdelegation a user may write a rule and ask another peer toprocess it remotely. Consider again the previous rule:attendeePictures@Jules($id, $name, $owner, $data) :-selectedAttendee@Jules($attendee),pictures@$attendee($id, $name, $owner, $data)Suppose we have the facts:selectedAttendee@Jules(“Émilien”)The evaluation of the rule leads to delegating the following ruleto Émilien:attendeePictures@Jules($id, $name, $owner, $data) :-pictures@Émilien($id, $name, $owner, $data)to send all the facts in his relation pictures to Jules. This isa simple case of delegation, which can be controlled by infer-ring access from the specifications described above. Howeverdelegated rules can be more complex, and general methods foreffectively controlling delegation are a topic of continued inves-tigation. The demonstration of Wepic will provide a simplifiedmodel for control of delegation, in which each delegation sentby an untrusted peer will be pending in a queue until the userexplicitly accepts it via the Web interface. A notification of apending delegation can be seen at the top of Figure 3, whereJulia is sending a rule to Jules. By default, all peers except thesigmod peer will be considered untrusted.4 Demonstration ScenariosWe now describe the general proceedings of the demonstration.The goal will be to share pictures taken during the sigmodconference. Émilien and Jules are attendees of the conference.They have used Wepic to install locally on their laptops a col-lection of pictures. They demonstrate how to use Wepic withthe native functionalities described in Section 3 and how to cus-tomize the application. They will also allow a user at the con-ference to run his own Wepic peer to explore the system. Thisscenario will demonstrate the various aspects of WebdamLog,notably distribution, delegation and control of delegation.Setup In the beginning of the demo, three peers are estab-lished: one on each of the laptops of Émilien and Jules, con-nected via a local network, and a third, the sigmod peer, hostedon Webdam cloud. To simplify the presentation, we will as-sume that Émilien and Jules organize their data and behavesimilarly. They both store their photos in pictures@Émilienand pictures@Jules on their respective Wepic peers. Both haveFacebook accounts and are members of the SigmodFB group,the official Facebook group of the conference. Finally, bothusers are subscribed to the sigmod peer, which stores the listof registered Wepic users.The Wepic peers Émilien, Jules and sigmod are depictedin Figure 2. We will start the demonstration by quickly goingover the setup, and will then ask the user to interact with Wepicaccording to the following scenarios.Interaction via Facebook To illustrate the interaction betweena Wepic peer and other Web services, we use a Facebook wrap-per. For instance, the following rule is used by the sigmodpeer to automatically publish, on the Facebook group of sig-mod, the pictures belonging to sigmod attendees who haveauthorized this action:pictures@SigmodFB($id, $name, $owner, $data) :-pictures@sigmod($id, $name, $owner, $data),authorized@$owner(“Facebook”, $id, $owner)Conversely, the sigmod peer will automatically retrieve thepictures with their comments and tags from the Facebook groupand publish them to sigmod peer. Note that the system thusallows any Wepic user to see or publish (via Wepic) pictures inSigmodFB even without having a Facebook account. A useronly needs to appropriately populate his authorized relation tocontrol Facebook publication.We will explain the WebdamLog rules that implementthese interactions to audience members. We will then showthat a photo uploaded by Émilien into his local relationpictures@Émilien is instantly published to pictures@sigmod,and then propagated to pictures@SigmodFB.Customizing rules The main advantage of a peer-to-peer sys-tem such as WebdamLog is the ability to customize a peer’sbehavior. Therefore the most novel trait of Wepic is that itlets the user customize existing rules and add his own rules.For example, a user who is interested only in the pictures thathave a rating of 5 would customize the rule of the applicationas follows:attendeePictures@Jules($id, $name, $owner, $data) :-selectedAttendee@Jules($attendee),pictures@($id, $name, $owner, $data),rate@$owner($id, 5)Redefining this rule will change the contents of the frame At-tendee pictures in Figure 1, which we will demonstrate. We willexplain this rule and its effect to audience members, and willthen allow them to customize the rule further, retrieving, e.g.,only pictures that were taken by a certain sigmod attendee, orin which only certain attendees appear.Illustration of the control of delegation To illustrate the con-trol of delegation, Émilien will attempt to install a rule at Jules’3Figure 3: The interface to a WebdamLog program running Wepic.peer. We will demonstrate that the system requires the ap-proval of Jules before installing the rule, and that the programof Jules is changed once the approval is granted and the rule isinstalled.Interaction via the Web Finally, we will invite audience mem-bers to launch their own autonomous Wepic peers in the Web-dam cloud, and to interact with their peer through a UI, usingtheir smartphone or a tablet that we provide. From that pointon, they will be able to use all features of Wepic described inSection 3, e.g., upload their conference photos to their own peer.In addition, they will be able to use the Query tab to launch oneof the pre-defined queries, or to write their own WebdamLogqueries and rules with the assistance of the demo authors.References[1] S. Abiteboul et al. The active xml project: an overview.VLDB J., 2008. 2[2] S. Abiteboul et al. A rule-based language for Web datamanagement. In PODS, 2011. 1[3] S. Abiteboul et al. Web information management with ac-cess control. In WebDB, 2011. 2[4] S. Abiteboul et al. Viewing the Web as a Distributed Knowl-edge Base. In ICDE, 2012. 1[5] S. Abiteboul et al. The webdamlog system. Technical re-port, Inria, 2013. http://hal.inria.fr/hal-00813300. 1[6] P. Alvaro et al. Consistency analysis in bloom: a calm andcollected approach. In CIDR, 2011. 2[7] É. Antoine et al. [Demo] Social Networking on top of theWebdamExchange System. In ICDE, 2011. 2[8] J. M. Hellerstein. The declarative imperative: experiencesand conjectures in distributed logic. SIGMOD Rec., 2010.2[9] A. Morishima et al. Cylog/crowd4u: a declarative platformfor complex data-centric crowdsourcing. VLDB J., 2012. 24

Rule-Based Application Development using Webdamlog

Rule-Based Application Development using Webdamlog

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