The Heart of Connection: Hypermedia Unifiedby Transclusion
Theodor Holm Nelson
can imagine few honors greater than a fac- for this ultimate union and generalization of litera- ing page to Douglas Engelbart’s; he is one ture and movies? Personally, I wanted a system for of the great men of our century and I love massively parallel creative work and study; more him dearly. Like Doug I have had a unified grandly, I sought to design the rightful literature and vision, of which today’s popular attain- art canvas of the future, creating a technical, legal ments are only centerless shadows of the and commercial basis for a worldwide populist and edge. But I have till now had little basis for participatory electronic literature of freely weaving conversation with the computer main- screen transmedia—republishable and quotable with- stream. Coining words has hardly helped (e.g., hyper- out restriction—to the betterment of human under- Itext, hypermedia, transclusion). standing and freedom of expression and access [2]. Let me begin again, for few have understood. What better dream at 23? After college, wishing to work alone as rogue And still a good idea. philosopher and film-maker, I was troubled about By the end of 1960 I Figure 1. Deep Inter- distribution for self-publishing and how to manage had a design paradigm comparison Viewing— notes and threads for many projects. Then I took a centering around deep Transclusion through computer course. Philosophically, I saw that the intercomparison. The Zipper Lists: Zipper lists computer was a clockwork of arbitrary abstractions resulting system design are a data structure and designable any which way; cinematically, I saw it (called since 1967 viewing method for would become the theater of all media turned inter- “Xanadu”TM) has always multithreaded items. active. These two angles fused into a stereo perspec- been a unified scalable Figure 1a shows item tive pointing far beyond. concept, both for per- A’s logical existence in What would be the best underlying abstractions sonal work environments three contexts. The user would view this as 1b’s equivalent zipper Multithreading of item A Zipper lists equivalent lists, with equality- bands indicating item Book Do to multithreading project Thursday A’s transclusion (virtual presence) in the three Book Smith contexts side-by-side. AAA A Thurs.
With Mrs. Smith item A virtually in three places (transclusion)
COMMUNICATIONS OF THE ACM August 1995/Vol. 38, No. 8 31 Engelbart continued each maintaining its individual identity). This great- ly extends the notion of manipulating sections and Integrated Applications: A tool system using a uni- subsections in today’s outlining tools. versal knowledge base replaces the standard applica- tion or function-based paradigm. Individual Every Object Intrinsically Addressable (Linkable to): application subsystems (graphical editors, program Every knowledge object—from the largest docu- language editors, spreadsheets) work with knowl- ments, to aggregate branches, down to content units edge products, but do not “own” hyperdocuments in such as characters—has an unambiguous address, the sense of being responsible for their storage or understandable and readable by a user, and refer- representation. For instance, one could create a enceable anywhere in the hyperdocument system. Gantt chart within a project management system, Such intrinsic addressability should be integrated and manipulate it as a graph in a charting applica- deeply into commands for editing, structuring, tion or as mail in an email application. An integrat- jumping. Intrinsic addressing options not only are ed core application package provides base natural to learn and embed in links, but serve as capabilities of composing, reading, annotating, link- parameters for direct, user-invoked jumping and ing and manipulating knowledge products. All manipulation commands. This addressing scheme knowledge workers—authors and users—modify and allows direct or indirect addressing (absolute or rela- incorporate other knowledge products into their tive, and through aliases; indeed we allow unlimited own information bases and knowledge products indirect address chaining) and working with objects (much as Ted Nelson advocates in Xanadu). not currently displayed. For instance, one can copy a structure without finding and opening the file con- Explicitly Structured Documents: Objects within a taining it. Meta-level referencing (addresses on links hyperdocument have an explicit structure in which themselves) enables knowledge workers to comment structural and logical substructures may be upon links and otherwise reference them. addressed and manipulated. For example, one can manipulate any statement in a hierarchical structure View Control of Form, Sequence and Content: A as an aggregate branch of all its substatements (with structured, mixed-object hyperdocument may be dis-
Nelson continued comprehension and study).1 Transclusion brings to electronic publishing a copyright method that makes (managing private versions) and for hypermedia republication fair and clean: Each user buys each quo- publishing— that is, all publishing. tation from its own publisher, assuring proper pay- The central idea has always been what I now call ment (and encouraging exploration of the original). transclusion, or reuse with original context available, Contexts of transclusions must be visually compa- through embedded shared instancing (rather than rable on screen as shown in Figures 1 and 2. (Unfor- duplicate bytes). Thus the user may intercompare tunately, today’s windowing systems do not yet allow contexts of what is re-used, both for personal work arrows and bands to cross frame boundaries.) (keeping track of reuse) and publication (for deep Such intercomparative use at the center of all digi- tal function meant building a Lugudunensis Durocortorum Argentoratum Regina Castra Snerd, I., Rome super D Quadi new kind of file Lige 83 a r A.D. n Decumate Augusta u r Figure 2. Deep i u s Vindobona As I See It. Vesontio Vindelicorum system. It would Augusto- Agri Lauriacom Avaricum Vindelicia Carnuntum dunum 15 Intercomparison GALLIA Raetia Norieum Aventicum Savaria be hyperarchical, Germania Curia 15 15 Lugudunum50 Virunum When Caesar said, Aquitania Pannonia Viewing—Trans- 222 10 A.D. 10 A.D. permitting the 222 A.P. D r iu Burdig 15 Mediolanium a s ala Vienna Aquileia Emona sup. inf. “ All Gaul is di- clusion and Link Taurasia Gallia Venetia same material to s Tergeste ILL si R.C. Placentis Cremona Mursa en 15 Siscia vided into three Display through Tolsa bon 121 Genua 191 be organized into Nar Nemausus A.M. Cisalpina D YRIC 14 154 Narbo Arelate 224 a parts,” he referred, Transpointing Massilia IT Ariminum l simultaneous Pisae 268 Salonae m Ilerda M first, to Trans-Al- Ancona a a Frames: Equality- r PHARUS Celtibert ALIA t alternative struc- Caesaraugusta e 219 Narona A 33 i pine Gaul, which Dertosa Corsica d a bands indicate Aleria r tures—hierar- Tarraco 238 Corfinium i Roma a Saodra t i we now know as the transclusion e u chies, sequences, Ibericum m 229 Sardinia Capua Canusium Apollonia southern France; of text across Valentia Mare Neapolis Tarentum hyperplexes. It 201 Baleares 238 Brundsium PITYUSAE secondly, to Cis-Al- window frames 123 Caralis Mare could permit no Carthage Alpine Gaul, now in two contexts. Tyrrhenum Croton embedded codes, Arrows show called part of Italy; would make all and third, much to links across win- Caesar, J. The Conquest of Gaul. changes by dow frames. the confusion of All Gaul is divided into three parts. optional additions and structural
32 August 1995/Vol. 38, No. 8 COMMUNICATIONS OF THE ACM Commentary played with a flexible choice of viewing options: References selective level clipping, filtering on content, trunca- 1. Engelbart , Douglas C. Toward high-performance knowledge tion or other transformation of object content, new workers. In OAC ‘82 Digest, Proceedings of the AFIPS Office Automation Conference. (Apr. 5--7, 1982, San Francisco) 279-- sequences or groupings of objects including those 290. Republished in Computer Supported Cooperative Work: A residing in other documents, etc. Links may specify Book of Readings, I. Greif, Ed. Morgan Kaufmann, San Mateo, views so traversal retrieves the destination object Calif. (1988) 67--78. /
overlay. As a deep revision server and project tracker work groups and make them smarter, I to free the for writers, scholars and programmers, it would man- individual from group obtuseness and impediment. age reuse and instance comparison in all projects and That we have converged on common ideas to any publications. Users trying many possible organization- degree is astonishing, and shows, I think, their cor- al strategies could maintain all of them to express the rectness and generality. C unified fullness of their exact ideas. And this single- user console would scale up directly to groupware References and a mighty on-line publishing server for tomorrow’s 1. Nelson, T. Transcopyright: Pre-Permission for Virtual Repub- transclusive all-media interactive literature. lishing, (1995), unpublished. Since then, colleagues and I have implemented 2. Nelson, T. Xanadu: Document Interconnection Enabling Re- (in varying degrees) half a dozen server designs, Use with Automatic Author Credit and Royalty Accounting. improving granularity (especially editability of Information Services & Use , 14 (1994). embedded instances), mechanisms of transclusion, 3. Nelson, T. Literary Machines, various editions; most recent is a Japanese translation, (1994), ASCII Press. Most recent English mechanisms of versioning, and transvisibility (the version: Literary Machines 93.1, Mindful Press, Sausalito, Calif. ability to reach different instance portions from one 4. Nelson, T. A file structure for the complex, the changing and another) [3]. Substantial funding was provided for a the indeterminate. In Proceedings of the ACM Twentieth Nation- time by Autodesk, Inc. [5] al Conference, (1965). Of late I have rethought the system’s core, which 5. XOC, Inc., Xanadu Hypermedia Server, Developer Documen- had always seemed irreducible. I now discern layers: tation, Mindful Press, (1992). project tracker engine, change manager, networking this and that, publication server, sale method, legal Best known for coining the words “hypertext” and “hypermedia” in the early 1960s, basis, among others. Separable specifications will help Ted Nelson considers his to be the third school of computer thought (after hierarchi- calism and AI but preceding Xerox PARC by years). Nelson’s theory of Virtuality everyone to build systems of this class on a mix-or- subsumes software under cinema as the design of seeming. match basis. I already have elucidated the copyright method—actually an open permission system—in a Xanadu, a name adopted about 1967, is a registered trademark of Project separate paper [1]. Xanadu. Like Doug Engelbart, I slog on with ideals held high above the mud. Ironically, Doug and I started 1 For sequences of discrete chunks, transclusion is isomorphic to multi- from completely opposite premises: he to empower threading items (see Figure 1 and [4]).
COMMUNICATIONS OF THE ACM August 1995/Vol. 38, No. 8 33