home mvc

MVC
XEROX PARC 1978-79

I spent a very happy and inspiring year as a visiting scientist with the Learning Research Gorup (LRG) at Xerox PARC from the summer og 1978 to the summer of 1979. This group was dedicated to Alan Kay's vision of the Dynabook; a portable computer that should contain all data of interest to its owner/user. Very importantly, these data included the programs the owner used to manipulate them. The owner/user should be able to understand and write the programs, thus gaining ascendancy over the computer.

The MVC notes should be read on this background. The user was the czar; everything done at LRG was done to support him. An earlier paper adds some background for MVC:

A note on DynaBook requirements
22 March 1979 (Partial scan, 11 pp
http://folk.uio.no/trygver/1979/sysreq/SysReq.pdf

I have sometimes been given more credit than is my due, so I should stress that I am not one of the original inventors of Smalltalk. I am only one of the very early and very enthusiastic users and contributors to this revolutionary innovation. I made the first implementation and wrote the original MVC note at Xerox PARC in 1978. The note defines four terms; Model, View, Controller and Editor . The Editor is an ephemeral component that the View creates on demand as an interface between the View and the input devices such as mouse and keyboard.

Jim Althoff and others implemented a version of MVC for the Smalltalk-80 class library after I had left Xerox PARC; I was in not involved in this work. Jim Althoff uses the term Controller somewhat differently from me. An important aspect of the original MVC was that its Controller was responsible for creating and coordinating its subordinate views. Also, in my later MVC implementations, a view accepts and handles user input relevant to itself. The Controller accepts and handles input relevant to the Controller/View assembly as a whole, now called the Tool.

The essential purpose of MVC is to bridge the gap between the human user's mental model and the digital model that exists in the computer. The ideal MVC solution supports the user illusion of seeing and manipulating the domain information directly. The structure is useful if the user needs to see the same model element simultaneously in different contexts and/or from different viewpoints. The figure below illustrates the idea.

MVC was conceived as a general solution to the problem of users controlling a large and complex data set. The hardest part was to hit upon good names for the different architectural components. Model-View-Editor was the first set:

Thing-Model-View-Editor
12 May 1979 (11 pp)
PDF (11 pp, 312,594 bytes)

After long discussions, particularly with Adele Goldberg, we ended with the terms Model-View-Controller:

Models-Views-Controllers
10 December 1979 (2 pp)
(.PDF (2 pp, 9,696 bytes)

The two papers have been copied together here:
(PDF, 396 567 bytes)

The Controller was here what I now call a Tool. The Smalltalk-80 Controller is here a fourth element called Editor. This was an ephemeral component that the View creates on demand as an interface between the View and the input devices such as mouse and keyboard.

The MVC problem has more facets than I realized in 1979. I started working on a pattern language to disentangle the different aspects, that last draft was dated August 20, 2003. The plan was that it should be improved by a group of authors, not just the current single one. Unfortunately, the projct died at his point.

MVC Pattern Language
.PDF (1 029 554 bytes)

Also see The Model-View-Controller (MVC ). Its Past and Present below: