Interactive Visual Exploration of the Regesta Imperii MarkusJohnmarkus.john@vis.uni-stuttgart.deUniversityofStuttgart,GermanyChristianRichterchristian.richter.rr@gmail.comUniversityofStuttgart,GermanySteffenKochsteffen.koch@vis.uni-stuttgart.deUniversityofStuttgart,GermanyAndreasKuczerakuczera@uni-mainz.deUniversityofMainz,GermanyThomasErtlthomas.ertl@vis.uni-stuttgart.deUniversityofStuttgart,Germany

Introduction TheAcademyofSciencesandLiterature inMainzprovidesonlineaccesstotheRegestaImperii-averyextensive historical dataset based on documentarysources of German-Roman kings. About 125,000regestae of emperors and popes are searchable andviewable in this online portal. The current userinterface offers direct access to single documentsthroughdifferentform-basedsearchfacilities,aswellas through a catalogue that directly reflects thestructureof the regestaevolumesas theyhavebeencreated in this long-termproject. Inorder to furtherimproveaccesstothislargedatavolume,wesuggestan additional approach based on coordinated views.The usage of coordinated view approaches is verycommon in many domains (Stasko et al, 2008,Vuillemotetal,2009,Kochetal,2011).However,thereisnopubliclysystemavailable,whichwouldprovideasuitable access to this historical dataset. Themotivation for this new approach is twofold.On theone hand, we improve the support for search andexploration tasks in this historical data set that are

based on imprecise information needs or on a lessdeep understanding of the available information. Inpractice,suchimprecisequeriescanquicklyleadtoanoverwhelmingly large number of search results.Allowinguserstocreateandrefinequeriesinavisualway, while offering immediate feedback on thenumber of entries requested, can help to cope withunderspecified queries and help refining themiteratively(Jänickeetal,2012).Ontheotherhand,weoffer a powerful means for visually analyzing theavailable information and understanding complexrelationships by providing different linkedperspectives on subsets of the collections. Theseperspectives include views on historic persons andentities as well as temporal and spatial informationcontained in the regestae. A usage scenario showssuccessfulapplicationoftheapproach.

Visual approach Weimplementedaweb-basedvisualizationthatiseasily available to humanities scholars, since it doesnot requireusers to install software.Theweb-basedvisualizationusesthelibraryData-DrivenDocuments(D3) (Bostock et al, 2011) and runs with a webbrowsersupportingHTML5,SVG,CSS,andJavaScript.

Data processing In the Regesta Imperii database all documentarysourcesofGerman-Romankings are available in fulltext (xml-files). This data set consists of regestaevolumesand register information.Regestaevolumesareshortsummariesofa textandcontain importantmetadata of a document, such as the title of thedocument, an ID for the unique assignment, date ofissue,andplaceofissueasnameandcoordinates. Since places, persons, and institutions may beknownbydifferentnames,entriescanbeoverlookedwithin the full-text search. Therefore, place andpersonalregistersprovideacentralresourceforworkwiththeregestaeandcontainalistofplaces,persons,institutions, and additional information, such as thenumbers of the regestae in which the entity ismentioned, a reference to another entity entry (ifavailable),andauniqueid. Since the regestae have been manually digitized,thexml-filescancontainsyntaxorothertransmissionerrors,suchasdifferentdateformats,geo-coordinatesor tags.Therefore, thedatamustbeparsedandwellpreparedinordertousethemforavisualanalysis.

Visual approach

Aftertheregestaeandregistervolumeshavebeensuccessfullyparsedandloadedintooursystem,userscan start their exploration in the main view asdepictedinFigure1.Themainviewconsistsofthefivecoordinatedviews: (A) timeline view, (B)mapview,(C) register view, (D) overview filter view, and (E)resultsview.

Figure 1. The interactive visualization approach for exploring

and analyzing regestae of royal and papal records.

We initially depict all available data and enableusers to create and refine queries in a visual wayiteratively, to reduce the overall set. For example,users can select certain time periods and places inwhich the regestae were published or persons andplacesthatarementionedintheregestae. Thetimelineviewconsistsoftwostackedtimelinesandenablesusers toselecta timeperiodbyclickinganddragging,asdepicted inFigure6,comparabletotheSimileapproach(Huynh,2008).Thefirsttimelineallows a coarse filtering and represents the whole-timerangeoftheregestae.Onceatimespanisselected,the second timeline is updated and permits a finerselectionoftheupperselectedtimerange. To get an overview where the regestae werepublished, users can discover the map view asdepictedinFigure2.ThemapviewusestheJavaScriptlibrary Leaflet (Agafonkin, 2014) which supportsinteractivefeaturessuchaszoomingandpanning.Thered circles in the map represent places where theregestaewerepublishedandthecirclessizeisscaledproportionallytotheplacesoccurrences,similartotheapproach (DARIAH-DE, 2015). This helps to get aquick overview of important places.When hoveringoveracircle,atooltipshowsthecorrespondingplacename.Byselectingoneormorecircles(highlightedinyellow),theplacesareaddedtothesearchquery.

Figure 2. The map view gives an overview where the

regestae were published.

Theregisterviewrepresentstheentitiesfromtheregister volumes in an alphabetically sortedhierarchical structure as depicted in Figure 3. Userscan explore the different entries by clicking on thedifferent hierarchies. Nodes, which contain furtherentities are displayed in darker color. Furthermore,users can select one or more entities to adapt thesearchquery.

Figure 3. The register view represents all persons, places,

and institutions which are mentioned in the regestae.

From the overview filter view, users can get asummary about all the selected places and entitieswhichdeterminethesearchresults.Inaddition,userscandeselectplacesandentitiesfromthelisttoadaptthesearchquery.

Figure 4. The overview filter view gives an overview of all

selected places and entities.

Based on the combined search query, the resultview lists all regestae entries,which are included inthe search results as depicted in Figure 5. For eachentry,thelistdisplaysthefollowingmetadata:titleoftheregesta,issuer,placeanddateofissue.Byclickingon the icon in the column entities, users get theinformationofallentitiesoccurringintheregestainaseparate list view.Furthermore,users can select theicon in the last column uri to jump directly to thecorresponding regesta entry on thewebpage of theRegesta Imperii. This enables users to analyze theregestaindetail.

Figure 5. The result view displays all regestae entries which

are included in the result set.

Usage scenario In the following section, we present a usagescenario that occurred during one of the jointworkshopsofusersfromtheAcademyofSciencesandLiterature in Mainz and the developers of theapproach. Therefore, our usage scenario representsinstead the insights and lessons learned throughseveral sessions with two experts from the RegestaImperii. Inafirststep,theexpertexploresandanalyzethemapview.Thatway,shegetsaquickoverviewoftheplaces where regestae were published. During theexploration, the place Nürnberg (Nuremberg) hasarousedherinterest,sinceshehasalreadyexaminedtheseentriesalongtimeago.Tofindoutmoreaboutthe regestae entries, she starts a search query byselectingNürnberg (Figure6A) in themapviewanddiscoversthesearchresults inresultview.However,theresultsetistoolargeforafurtherdeeperanalysis.Therefore, she refines the search query by selectingthetimeperiodfrom1440to1450inthetimelineview(Figure6B),becausesheisespeciallyinterestedintheearlyregestaeentries.Asthenextstep,shesearchesforentitiesthatarementionedintheregestaewiththeaid of the results view. She finds out that there aremany connections to French entities. To furtheranalyze that, she selects the hierarchy “Frankreich,Königreich”(France,Kingdom)intheregisterview,asdepictedinFigure6C.Byadjustingthesearchquery,shereceivedaspecifiedsubsetofthecollectionforafurther analysis. This way, she finds that primarilyFrenchkingsarementionedintheregestaeentries.

Duringtheanalysis,shelearnsfromthemapviewthat Neustadt near Bremen (Figure 6D) has manyregestaeentrieswhichshedidnotexpect.Toinspectthis in detail, she selects Neustadt and explores theresultlist.ByanalyzingthedifferententriesinthelistandwebpageoftheRegestaImperii,shefindsoutthatthe geo-coordinates were manually digitizedincorrectly. Consequently, the expert corrects theentries in thedatabaseby assigning these entries totheactualplaceNeustadtnearVienna. Whilethesesessions,wereceivedalotoffeedbackthatshowedthatourapproachimprovesaccesstothelarge data volumes of the Regesta Imperii andfacilitates search and exploration tasks, as well asassistinginunderstandingcomplexrelationshipsandgainingnewinsights.

Figure 6. An example search query for the place Nürnberg,

French entities, and the time period from 1400 to 1440.

Conclusion and future work Thepresentedinteractiveweb-basedapproachhasbeen evaluated through expert feedback thatrecommendsitasaneffectivemethodforexplorationanalysis. We are planning to extend the different linkedviews to support users with additional information.Concerning this issue, we have implemented therelative distribution of the regestae volumes in thetimeline view, as depicted in Figure 6, and we arecurrentlyworkingontheco-highlightingbetweentheviews. We will also ensure that experts from theRegesta Imperii are able to correct errors that ariseduringthedigitizationprocessinteractively.

Figure 7. Timeline filter view of the selected year 1468 with

a relative distribution of the regestae over time.

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