\begindata{text,271714732} \textdsversion{12} \template{default} \define{symbola attr:[FontFamily symbola Int 0]} \majorheading{The Evolution of turnin A Classroom Oriented File Exchange Service } William Cattey (wdc@athena.mit.edu) MIT Project Athena 1 Amherst Street E40-349 Cambridge MA 02139 (617)-253-0140 \majorheading{Abstract} From the beginning, MIT Professors wanted to use the Project Athena campus wide computer network to collect assignments. The \italic{turnin} program started off as a shell script that sent files to a central timesharing host for perusal by a grader. When timesharing hosts were replaced by a network of workstations, \italic{turnin} became a network service layered on NFS. At that time, programs were added to help graders sort through the files. Student retrieval of prepared handouts and the exchange of papers in real-time were added. Today, \italic{turnin} is a stand alone network service with cooperating servers and a replicated database. It has been integrated with a WYSIWYG editor for composition of complex documents, and their annotation by peers and teachers. The teacher side of the interface is evolving into a point and click gradebook interface. This paper describes the evolution of \italic{turnin} from its original shell script form to its current integrated editing/formatting/annotating system. \bold{\bigger{Introduction}} Project Athena exists to deploy and maintain a campus-wide network of workstations and services (such as remote file access, printing, and electronic mail) to MIT for educational use. In addition to deploying workstations and linking them together with the network, Athena develops software of general use to the MIT community, for example new system services (such as the \italic{Zephyr} notification service [DellaFera1988]), and educational software programs such as TODOR [Murman1988]. The \italic{turnin} system is both a file exchange system service and educational software. It was developed in response to the request of MIT professors who wanted to use Athena to manage electronically submitted assignments. The first version supported student submission of assignments, and teacher return of annotated assignments or new files. Subsequent versions offered more capabilities: real-time exchange of files in class, distribution of handouts, organization of papers to grade for the teacher, and integration of file exchange with document preparation. This paper chronicles \italic{turnin} from its beginning as a "silly little rsh script" to its present integrated application. \section{1 Version 1: "the rsh hack" } The first version of the \italic{turnin} service had the least functionality, the worst user interface, and the most difficult set up process. It was first used in the early days of Athena before workstations were installed. At that time Athena consisted of 63 networked timesharing hosts. The path followed by student papers is shown in Figure 1. Files exchanged through \italic{turnin} would start in the student's home directory on their assigned timesharing host. The \italic{turnin} program would send the file over the net to a sub-directory associated with the course on the teacher's timesharing host. The teacher would find the file, probably move it to his or her home directory, manipulate it, (perhaps compile it, perhaps edit it), and then move it to the course's pickup subdirectory, where the student could find it when he or she ran the \italic{pickup} program. \begindata{zip,272148332} %ViewWidth 371 %ViewHeight 196 *D;-1400,896 N8.5X11 >-1400,896 *G;-1550,800 >-400,-800 *G;300,791 >1500,-800 *A;-1000,650 Fandy10 TStudent Host MCM *A;850,650 Fandy10 TTeacher Host MCM *A;-1000,500 Fandy10 Tstudent/home MCM *A;900,500 Fandy10 Tcourse/TURNIN MCM *A;850,250 Fandy10 Tcourse/PICKUP MCM *A;900,-500 Fandy10 Tteacher/home MCM *A;-1100,300 Fandy10 TFile MCM *O;-800,296 >783,405 *A;-100,396 Fandy10 T1 MCM *O;900,396 >1400,396;1400,-704;900,-704 *O;700,-704 >400,-704;400,-104;800,-104 *O;763,-16 >-1000,196 *A;-100,-4 Fandy10 T4 MCM *A;1316,-67 Fandy10 T2 MCM *A;500,-304 Fandy10 T3 MCM *J;850,396 G100 >25,0 *J;850,-54 G100 >25,0 *J;816,-667 G100 >25,0 \enddata{zip,272148332} \view{zipview,272148332,31,0,198} Figure 1: The Paper Path \subsection{1.1 Why not electronic mail? } Other communication services developed at Athena such as \italic{discuss} [Raeburn1989], and \italic{Zephyr} [DellaFera1988] were not implemented as electronic mail because they required services that electronic mail did not provide. (Instantaneous transmission in the case of \italic{Zephyr}, and central sequenced storage of messages in the case of \italic{discuss}.) With \italic{turnin}, the primary issue was user interface. Professors wanted a user interface that more closely resembled the traditional "hand it in, mark it up, give it back" classroom process than existing exchange systems such as electronic mail and network filesystems did. The service could be built on top of a network file system, the mailer, or any other available communication system as long as professors and students felt comfortable exchanging papers with it. For example, they didn't want to deal with mail headers in papers. In the simplest application, students would compose documents. These documents would be annotated by the teachers. The annotated documents would, probably, be re-used by the students for later drafts. Some professors wanted to receive executable files to run rather than papers or program listings to read. This imposed the constraint that the transport mechanism be able to exactly reconstitute the bits of the submission, but even this was not necessarily difficult to do with an appropriate user interface to the mailer. We decided against using the mailer because it was not well suited to use as a file repository. The Athena Post Office Service is based on the assumption that neither the mail hub nor the post office machines are used to store mail for long periods of time. They are configured for relatively small amounts of storage that is constantly reused. \subsection{1.2 The Student User Interface } Students were expected to use the UNIX timesharing host to do their work and exchange it with professors using these two commands: \example{turnin problem_set file [file] } and \example{pickup [problem_set] } The \typewriter{problem_set} argument was a string to name the problem set. Often this would be specified by the teacher. The file arguments could also be directories. If \italic{pickup} were called with no argument or if the named problem set was not found, a list of existing problem sets to pickup was returned. \subsection{1.3 The Teacher Non-interface } The only professors who used \italic{turnin} were UNIX cognoscenti or had teaching assistants who would do all the computer work for them. One course only used \italic{turnin} as a way to collect assignments. A TA would send the assignments to the line printer and take the printouts to the grading meeting. To annotate files the teacher was expected to know the \italic{turnin} file hierarchy and to use UNIX commands to obtain the file, edit it, and save the changed file in a similarly structured pickup hierarchy. Here is an example of what the file hierarchy might look like for a course, say, intro with two students jack and jill: \example{intro/ TURNIN/ jack/ first/ README foo.c second/ Makefile foo1.c foo2.c jill/ ... PICKUP/ jack/ first/ foo.errs second/ a.out.errs jill/ ... } Organizing papers this way posed a problem. Most MIT professors are expert in their own fields, not in computers. Many found the hierarchy difficult to navigate and not well matched to their methods of organizing student work. This tended to make the teacher's job harder, while the goal of \italic{turnin} had been to make it easier. \subsection{1.4 The Transport Mechanism } The first version of \italic{turnin} relied on a primative mechanism for transfering data. Users of Berkeley UNIX may be familiar with the following command line to duplicate a hierarchy on a remote host: \example{\smaller{tar cf - | rsh remote.host "(cd destination/directory; tar xpBf -)" }} On the timesharing host that was to receive papers, a special account called "grader" was created. Instead of /bin/csh like everyone else, grader's login shell was \italic{grader_tar}. This program relied on receiving as arguments: \leftindent{ \symbola{7} a flag to determine if this was a turnin or a pickup \symbola{7} the student's username \symbola{7} the hostname of the machine the student was on \symbola{7} a name for the problem set \symbola{7} the absolute pathname of the student's working directory \symbola{7} the name of the file or directory being transferred. } It used this information to locate the files to transfer, and to set the student's host as the remote.host to rsh to. The \italic{turnin} program would \typewriter{rsh -l grader }passing it these arguments, and the \italic{grader_tar} program would rsh back to the host that initiated the \italic{turnin} to perform the transmission! \subsection{1.5 Security } Care was taken to prevent unauthorized access to turned-in files. The course \italic{turnin} directory was accessible only to members of a file protection group which was specially made for each course, and to the magic grader account. The grader.tar program relied on rsh for security. The \italic{turnin} program would modify a .rhosts file in the student's home directory to allow the grader.tar's rsh to succeed. There was no global trusting among the timesharing hosts. Probably the best enforcement of security came from the obscurity of the program. It was hard for the installers and developers to retain a clear idea of how it worked. This security through obscurity proved adequate for our prototype, but it was unacceptable for a \italic{turnin} service in wide use. \subsection{1.6 Problems } The \italic{turnin} prototype was an interesting experiment in using the Athena timesharing hosts to exchange papers electronically, but as a service it left much to be desired. It had problems in setup, maintainability, and usability. The maintenance headaches came from teaching new people how to set up \italic{turnin}, and in controlling the amount of disk taken up by the course. Setup required establishment of the grader account on the timesharing host, and installation of the user programs in course program libraries. The location of the course \italic{turnin} directory had to be established and placed in a file along with the \italic{turnin} program in the course program libraries. Athena User Accounts had to create a group for the graders, and keep it up to date. Student user id's had to be known to the course timesharing host, even if the students were not allowed to log on to it. Disk consumption had to be monitored by a person periodically running \italic{du} over the course directory. Usability was the biggest problem. A grader interface for those who were not UNIX literate was needed. It had to help rather than hinder the organizing of student files. The time delay in depositing files needed to be reduced. Other activities closely related to collecting and returning papers could also be supported. The real reason why \italic{turnin} version two came about, however, was the demise of the timesharing hosts, and the elimination of rsh as a transport mechanism. \section{2 Version 2: Expanded Functionality } In spite of the problems with the user interface, \italic{turnin} acquired a small but loyal following of satisfied customers. Athena decided to try and keep these customers when the timesharing model of computing was replaced with the distributed services model. Our challenge as \italic{turnin} developers was to find a new file exchange mechanism not based on rsh that would work in the environment of non-secure workstations contacting secure service hosts. The person assigned to do the new version of \italic{turnin} was concurrently working with the MIT writing faculty on another project. He saw an opportunity to expand turnin; to market it to new users while at the same time completely re-implementing the old service. This follows the great MIT tradition, "We can't solve that problem, but we can solve another much harder problem." The MIT writing faculty had formed a group, the Committee on Writing Instruction and Computers (known as CWIC, pronounced "quick"). This group met weekly to discuss ways that computers, specifically those offered by Athena, could be applied to improve writing instruction at MIT. This group came up with four basic activities of writing instruction they wanted the computer to support. In a writing class, students and teachers: \leftindent{\symbola{7} create texts \symbola{7} exchange texts \symbola{7} display text \symbola{7} critique, annotate, and discuss texts } A specification, \italic{Electronic Classroom: Specification for a User Interface} [Barrett1987], was written based on the group's work. The second and third versions of \italic{turnin} were based on this spec. Starting from the principle of computer enhancement of common activities in class, six components were called for: \leftindent{1. A \bold{Classroom Put and Get Program} to pass files between students during class. 2. A \bold{Grade Sheet} interface for assignments to provide a simple method for an instructor to organize and correct student assignments. 3. A \bold{Syllabus} interface for handouts to organize these files in an easy to use format and to permit instructors to add or modify curricular files for in-class use. 4. A \bold{Turnin} interface for turning in and picking up assignments and handouts. This interface simplifies current protocols for submitting assignments and picking up annotated papers or other class handouts. 5. An \bold{Electronic Textbook} facility that permits the storage of a set of files representing class notes, instructions and other reference material. 6. A \bold{Presentation Facility} to format files for display on a screen projection device, (i. e. Show the file on the workstation screen in a big font so it will be legible when displayed in class with a screen projection system.) } Component number four represented a re-affirmation that the old \italic{turnin} would be useful. The new version of \italic{turnin} would implement as services the new components one, two, and three as well as re-implementing number four. The "Grade Sheet interface" of component two specified how organizing student papers would be improved for teachers not literate in UNIX. The files managed by the new version of \italic{turnin} were organized into three classes: \leftindent{\symbola{7} exchangeables -- for component one, the in-class put and get facility \symbola{7} gradeables -- for components one and four \symbola{7} handouts -- for component three } The file exchange system was designed to support these and future classes of files so that user interfaces could be tailored to the kind of file being exchanged. The whole system of six components, and the procedures and protocols for applying them in the course of writing instruction were collectively called EOS the \bold{E}ducational \bold{O}n Line \bold{S}ystem. \subsection{2.1 Turnin on top of NFS } The spec was completed on 3 June 1987 and handed off to the development team. The team consisted of Maria Camblor, Bruce Lewis, and Rob Shaw with me as project manager. The timesharing model of computation at Athena was to be replaced by the distributed services model of computation on 1 September 1987. What sort of software could we offer as a robust implementation of the spec in three months, given that none of the team members had ever written a network service before? It was initially unclear what sort of new transport mechanism was to be used in Athena's new distributed services environment. We decided not to use the mail system for reasons described above. Athena had recently deployed its \italic{discuss} service [Raeburn1989]. We opted not to use the discuss protocol because generating lists of student papers would take a long time, all the papers would be kept in one large file, and utilities to allow old style UNIX command oriented manipulation would be hard to write. We decided to access the server through a client library (which we named FX.) This would allow the same application programmers interface regardless of what transport mechanism we used. We expected to throw our first server away. We believed that the best way to offer the file exchange service was via a remote procedure call, much like the successful X server. We studied the Sun Remote Procedure Call system and felt it was the right implementation scheme, but were concerned that it would take too long to write and test such a server. As described below, we opted for a much simpler implementation strategy. We agreed on the FX library calls by studying the spec and by designing the user programs. While Maria Camblor and I set about designing the server and implementing the client library, Rob Shaw and Bruce Lewis wrote the student programs and the teacher programs respectively. We documented our design for use by later developers [Camblor1988]. \subsection{2.2 The Clients } The student programs ended up resembling the original \italic{turnin} programs. There were three major differences: Assignments were changed to be numbers rather than names. Teachers asked to organize papers by class week number. The course was specifiable by a command line argument and an environment variable. New commands were added for the two new classes of files. The student commands were: \leftindent{\bold{put} - store a file in the in-class bin of files to exchange \bold{get} - fetch a file from the in-class bin of files to exchange \bold{take} - fetch a teacher created handout file \bold{turnin} - deliver assignment file \bold{pickup} - retrieve corrected assignment files } The student executed these programs from the shell when it was time to fetch or store a file. The teacher program was started once and had its own command parser. It enabled the teacher to create handouts, administer the class list, and to read, annotate, and return files. There was a list of commands for each of the three functions: grade: \example{\smaller{list, l list files turned in whois, who find a student's real name display, show display a file annotate, ann annotate a file return, ret, r return annotated file to student editor change or display current editor purge, del, rm remove turned-in file from bins man, info display information on a command }} hand: \example{\smaller{list, l list handouts whatis, wha show note for a handout put, p copy a file to a handout note, n add a note to a handout take, get, t copy a handout to a file purge, del, rm remove handouts }} admin: \example{\smaller{add add a name del delete a name list, l list all names in course }} The teacher would type the command and arguments. At any time the teacher could type "?" and get a list of the commands and a reminder of what the arguments were, or use the info command for more detailed information. The trickiest part of using the grader program was in specifying files. If no files were specified, the program would assume that all were to be manipulated. To restrict operation the teacher would give a file specification with four parts separated by commas as the argument: 1. assignment number (abbreviated as) 2. author user name (au) 3. version number (vs) 4. file name (fi) So commands like list taking a file name would have a reminder like this: \example{list [as,au,vs,fi}] An empty field matched all, so \example{list 1,wdc,, } would list all files turned in by user "wdc" for assignment 1. The administrative commands were installed to enable teachers to establish a class list. Only students in the class list were allowed to turn in or exchange files. The faculty found it inconvenient to maintain a class list on the computer, and the administrative commands were dropped from the grader program after a short amount of use. The actual workings of access control was de-coupled from the class list as described below. The important functions were display, annotate, and return. The display command was used for showing files in class. It would fetch the specified file from the server and use a settable display program to view it. (e.g. \italic{more}, \italic{vi} or \italic{emacs}) In practice a special \italic{emacs} with a large font was used as the display program. The annotate and return functions were used to bring the turned-in file into an editor such as \italic{emacs} and to return the modified file to the student. These commands were smart enough to be able to fetch and store multiple files. \subsection{2.3 The Server } We had insufficient time and experience to write a bona fide server. Instead, the client library attached an NFS filesystem, and implemented all the client calls as file operations. These NFS filesystems would be mounted when the application programs used the \typewriter{fx_open} call to begin, and unmounted when the \typewriter{fx_close} call was made, or when the program exited. This operation is consistent with operation of a network service. We planned to implement access control lists, but abandoned them too due to lack of time and experience. Jon Rochlis looked at the old \italic{turnin} hierarchy and suggested a way to use the standard UNIX file protection modes for access control. The method relied on the newly developed group access authentication that had been added as an Athena local change to NFS. The NFS filesystems were organized as follows: \leftindent{\symbola{7} Each course had its own NFS directory which was attachable by name. \symbola{7} There was a subdirectory for each type of file: turnin, pickup handout, and exchange. \symbola{7} Each of these directories was group owned by a file protection group created specially for the course. \symbola{7} All of the graders were in this group, and no student taking the course was. \symbola{7} The exchange directory was world readable and writable \symbola{7} The handouts directory was grader writable and world readable \symbola{7} The \italic{turnin} and \italic{pickup} directories were not world readable, but were world searchable and world writable. \symbola{7} The first time a student ran \italic{turnin}, a directory owned by him or her, inheriting the group ownership, but inaccessible to the rest of the world, would be created in the \italic{turnin} and \italic{pickup} directories \symbola{7} All turned in files and files to be picked up would live in the student owned subdirectories. \symbola{7} We used the 4.3bsd "sticky bit hack" to restrict file deletion to directory owners, even when the directory is labeled writable. Students could add themselves to the course but could not delete themselves or anyone else. } This had the effect that students could not find out who else's files were on the server, they could only write files into the \italic{turnin} directory, and would have trouble finding them to modify. They certainly could not read or modify other students files. The graders had free access to all the files. By attaching the course directory by hand, it was possible to create bogus \italic{turnin} directories potentially locking out students. But the perpetrator would own the directories and could be traced. The file hierarchy looked like this (for a single student, wdc): \example{\smaller{total 4 -r--r--r-- 1 jfc coop 0 Aug 9 1988 EVERYONE -rw-r--r-- 1 jfc coop 0 Aug 9 1988 List drwxrwxrwt 2 jfc coop 512 Aug 9 1988 exchange drwxrwxr-t 2 jfc coop 512 Jan 11 1989 handout drwxrwx-wt 3 jfc coop 512 Aug 13 1988 pickup drwxrwx-wt 3 jfc coop 512 Aug 9 1988 turnin exchange: total 0 handout: total 23 -rw-rw-r-- 1 wdc coop 559 Jan 11 1989 1,wdc,0,avl.h pickup: total 1 drwxrwx--- 2 wdc coop 512 Jan 11 1989 wdc pickup/wdc: total 16 -rw-rw-rw- 1 wdc coop 1474 Aug 15 1988 1,wdc,0,bond.fnd turnin: total 1 drwxrwx--- 2 wdc coop 512 Jan 11 1989 wdc turnin/wdc: total 16 -rw-rw---- 1 wdc coop 1474 Aug 15 1988 1,wdc,0,bond.fnd }} The class list (later abandoned) was kept in the file List. The existence of a file named EVERYONE signified that access was unrestricted. The owner of EVERYONE had to match the owner of the directory it was found in (to prevent just anyone from setting EVERYONE). Using the clever NFS access modes, we wrote the server and FX client library in two weeks. We met the user level spec with command line oriented programs: the familiar \italic{turnin} and \italic{pickup}. We added put and get for in-class file exchange, and \italic{take} for teacher created handouts. Our crowning achievement was \italic{grade}, a command oriented subsystem for finding new papers bringing them into an editor, and then returning modified papers. \subsection{2.4 Problems } This version successfully addressed the problem of usability. The teacher input from CWIC enabled us to provide a better user interface, and enhanced functionality. Retaining the old hierarchy allowed teachers who were comfortable with UNIX to grade as they had in the past, by attaching the NFS course directory manually. The major usability problem remaining was the long time it took to generate lists of files. Since the files were spread across several directories, the FX library did the equivalent of a \italic{find} to locate all the new files. The \italic{turnin} suite of programs were, for the most part, simple, but could have been better integrated into the flow of the classroom. Typing commands could perhaps have been replaced by clicking the mouse. The problems of setup and maintainability persisted. Controlling disk use became much more of a problem. The new problem of reliability arose: There was no graceful degradation of service in the face of NFS server failure. Disk usage had to be either monitored carefully, or had to have a lot of slack. If one student turned in enough to consume all the disk space, all courses using that NFS partition for \italic{turnin} would be denied service. Since the \italic{turnin} file repository was a single directory hierarchy manipulated directly by the FX library, there was no mechanism for having secondary storage places if the course directory could not be written into. Even if secondary storage was available, no thought was given to merging primary and secondary storage places, nor to being able to tell when all storage places were accessible. If the one NFS directory was full, or if the particular server was down, that entire course was denied \italic{turnin} service. The \italic{turnin} service put a strain on the Athena operations staff. The staff was only funded 9AM to 5 PM five days a week. Students would turn papers in 24 hours a day, seven days a week. If the NFS server went down, no paper could be turned in. In order for all courses to perceive \italic{turnin} service to be working, \italic{all} NFS servers holding \italic{turnin} directories had to be working. The reliability of the NFS based \italic{turnin} system became difficult to maintain near the end of every term when the entire Athena system received its heaviest load. The \italic{turnin} servers became heavily used with students turning in final papers, filling up the course directories when the operations staff is spread thin keeping the whole system up. Our NFS servers used the Berkeley 4.3bsd quota system used to monitor disk consumption. This implementation of quota clashed with the mechanisms \italic{turnin} used for access control. Since quota was by userid and since access was controlled by having students own their turned in files, quota would have to be set for each individual student. Professors found it onerous to use the grader tools to keep an on-line class list. Having to continuously advise Athena User Accounts of changes in the class was out of the question. Creating a default quota for all students on a particular server would not have helped much. It would have been difficult to come up with a default number of disk blocks to allocate because some students were in more than one course, and some courses required bigger files than others. Although it would have solved the one failure mode mentioned above of one student denying \italic{turnin} service, other modes of failure occurred more often. We never observed one student turning in a large block of files, but we often observed professors saving all student papers over a term and running the disk out of space. Until some mechanism of group quota or access control by list rather than owner were developed, quota was disabled for course directories that used \italic{turnin}. Someone on the Athena staff was assigned to watch over the disk usage. We worked around disk space problems by spreading out course directories among several NFS servers, dedicating large partitions to the non-quota directories, and having one person spend a lot of time watching the disk usage. We tried to limit course directories to 50 meg in a term, and to keep in contact with professors so that they could delete files before space became a problem. \section{3 Version 3: The Network Service } Whereas no more than 3 courses used the first version of \italic{turnin}, a dozen used the second version and more were expected in the future. The service was proving useful and was expected to become popular. This meant that something had to be done to solve the operational problems. This stand-alone version was written by Rob French. Bruce Lewis, Clifford Tse, and I contributed. The new version had to retain or improve upon the previous version's functionality, security, and speed. For example, several courses were exchanging files in class in real time, and collecting handouts at the beginning of class. This real-time performance had to be retained. The new version had to allow for easier server management. It had to allow: \leftindent{\symbola{7} simpler setup. \symbola{7} automated monitoring, and control of disk space usage through some quota mechanism. \symbola{7} graceful degradation rather than total denial of service in the face of server failures. } We proposed to write a new back end for the FX client library that would meet these requirements. \leftindent{\symbola{7} It was a true client/server model of service. \symbola{7} It was layered on top of the Sun remote procedure call protocol. \symbola{7} It contained its own access control list system. \symbola{7} Files were owned by the server daemon userid. } \subsection{3.1 The Server } The Sun Remote Procedure Call protocol was a commonly available mechanism for implementing a network service. Other protocols such as the Apollo Remote Procedure Call protocol could have been used. We chose Sun RPC because it was available, Rob had experience with it, and it seemed that its use was becoming more widespread. The access control lists are maintained in a database under the control of the server. Previously, access control relied on the Athena method of creating credentials files which were updated nightly on all NFS servers. Intervention of Athena User Accounts and a significant time delay were required to offer \italic{turnin} service to new courses, or to modify the list of qualified graders. With the \italic{turnin} server taking direct responsibility for access control, changes are made through simple applications, and take effect almost instantaneously. The head TA of a course can now add new graders. He or she needs no other special privileges or training. A new course can be created and used right away. Having the server daemon own all the files is not a very good solution. If each course is arranged as a separate partition or volume, a quota for the daemon userid can be established. It would be a simple matter to make the server run setuid root and to be able to set the file ownership to a particular userid for quota purposes. Perhaps the best solution is to add quota management to the access control lists so that the quota establishment, too, can be an instantaneous process divorced from Athena User Accounts. We made the following additional changes: \leftindent{\symbola{7} A database now stores the list of files along with their various attributes such as author, assignment number, and timestamp. \symbola{7} The server database remembers identities of files on other servers. \symbola{7} Servers cooperate and keep replicated copies of a common database } Taking advantage of our experience, we changed the FX library a bit. Instead of storing an integer version number for the file, a hostname and timestamp were associated with it. This simplified establishing a version identity in an network of cooperating servers. Lists of files were returned as handles on linked lists rather than simple linked lists to ease storage management and passing of data over the network. We documented our new client library [Lewis1989]. The basic operations were retained: \leftindent{\symbola{7} send a file \symbola{7} retrieve a file \symbola{7} list files matching a template \symbola{7} list access control list \symbola{7} add to access control list \symbola{7} delete from access control list. } The database is layered on \italic{ndbm}. We rely on ndbm to allow an efficient scan of the entire database when we generate lists of files. Although a sequential scan of an entire database is slow, it is always faster than a find over a filesystem with the same number of nodes. So although this algorithm is slow, the perceived benefit is great. If very large courses are to be supported, this simple approach to database management can be replaced with a relational database which would allow matching on the various file parameters. The database records information on the host responsible for holding the file, and there is a multi-server configuration that enables an authoritative database to be elected, and then shared among cooperating servers. The algorithms for electing and sharing are based on a simplification of the Ubik database system used in the Andrew Filesystem protection server. \subsection{3.2 The latest user interface } The original file exchange service used the GNU Emacs text editor with additional commands for annotating and displaying texts. The latest user interface integrates displaying, editing, formatting, exchanging, and annotating into two applications: \italic{eos} for the student, and \italic{grade} for the teacher. The student application gets its name from the \bold{E}ducational \bold{O}nline \bold{S}ystem, the term coined for the suite of programs and protocols specified for supporting the classroom activities. Here at last is one program, containing all the pieces, worthy of the name of the whole system. The teacher program gets its name from the command oriented grader program of the previous version of \italic{turnin}. These applications take advantage of the Andrew Toolkit (commonly called ATK) developed at Carnegie Mellon University [Palay1988]. ATK offers the following features which made it particularly useful in building \italic{grade} and \italic{eos}: \leftindent{\symbola{7} simple object oriented programming paradigm with inheritance to enable development by extending existing toolkit objects \symbola{7} graphical user interface management system building blocks to support development of point and click applications \symbola{7} rich selection of objects \symbola{7} available on the X tape \symbola{7} multi-font text object designed to look to the user like Emacs \symbola{7} dynamic object loader for small initial application size, and simple expansion as the user uses advanced capabilities \symbola{7} rapid application prototyping system. } Nowadays many people are developing graphical applications. Developing X based applications with object oriented toolkits has become de regueur. Availability on the X tape allows more freedom than proprietary development platforms, and a rich selection of objects increases the likelihood that the developer can use existing toolkit code rather than writing new code. The multi-font text object was crucial. Virtually all multi-font text objects suitable for use as a stand alone text editor are extremely proprietary. We have not seen any other that has a code size under 1Meg. The ATK text editing objects are small, efficient, and extensible through the dynamic object loading system. We like being able to offer users the ability to edit equations, spreadsheets, and line drawings in \italic{eos} without requiring all users to start up an \italic{eos} containing all those subsystems. Until the time when students all run 12 MIP machines with 16 Meg of main memory, ATK offers an extremely attractive balance of size versus speed that no other toolkit has approached. The original version of \italic{eos} was done by N. Hagan Heller for her S. B. thesis at MIT in the department of Computer Science and Engineering [Heller1989]. She used the \bold{A}TK \bold{D}evelopment \bold{E}nvironment \bold{W}orkbench (ADEW) to do her prototype. The ADEW system allowed her to compose and modify her screen layout directly with a WYSIWYG interface. Although we opted to re-implement her prototype in raw ATK toolkit calls, we could have used the ADEW code generator to build the application. We chose not to use ADEW because of some restrictions that ADEW imposed which have, for the most part been removed. Nick Williams, of Imperial College, University of London, visiting MIT for the summer re-implemented Hagan's design with assistance from me. Nick's implementation is outlined in an EUUG talk [Williams1990]. The five student file exchange programs (\italic{turnin}, \italic{pickup}, \italic{put}, \italic{get}, and \italic{take}), the editor, GNU Emacs, and the formatter (which was most often not used because it interfered too much with annotating) were made into an ATK editor with buttons across the top. Figure 2 shows \italic{eos} with a typical short paper: \begindata{raster,272362128} 2 0 58514 58514 0 0 504 405 bits 272362128 504 405 ZZZI | ZZZI | e2(2223)2232(22 23)222a(2226(22 23 | c8(888b)88b8(88 8b)8898(888c(88 8f | e2(2225)2252(22 25)221a(2236(22 27 | c8(888f)88f8(88 8f)88f8(88bc(88 9f | e2(aaab2a(aab2 (aaab2a)aa2a'aa ae2a'aaab | c9(555f85(55f8 (555f85(55f8d5 '557c95'557f | e2(aab52a'aaab 52(aab52a(aa5a 2a'aad62a'aa97 | c9(555f85(55f8 (555f85(55f8d5 '557c95'557f | e2(aaab2a(aab2 (aaab2a)aa2a'aa ae2a'aaab | c9(555f85(55f8 (555f85(55f8d5 '557c95'557f | e2(aab52a'aaab 52(aab52a(aa5a 2a'aad62a'aa97 | c9(555f85(55f8 (555f85(55f8d5 '557c95'557f | e2(aaab2a(aab2 (aaab2a)aa2a'aa ae2a'aaab | c9(555f85(55f8 (555f85(55f8d5 '557c95'557f | e2(aab52a'aaab 52(aab52a(aa5a 2a'aad62a'aa97 | c9(555f85(55f8 (555f85(55f8d5 '557c95'557f | e2(aaab2a(aab2 (aaab2a)aa2a'aa ae2a'aaab | c9555f96556556 5d!555f85557f 95!5557"55f856 59!5556#555f85 7f955575$55f8 d5555795575595 !557c95!55d755 75"557f | 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The teacher interface, \italic{grade}, looks just like the student interface except that the \italic{Turn In} and \italic{Pick Up} buttons are replaced with \italic{Grade} and \italic{Return} buttons. The \italic{Guide} button opens a window on an on-line style guide that is being experimented with by the writing teachers who use eos. It replaces a GNU Emacs based on-line style guide that was too hard to use. The new one uses hyper-link buttons to access a whole lattice of information. The \italic{Help} button is used to start the ATK \italic{help} documentation browser. When a student clicks \italic{Turnin}, a dialogue box pops up to get the filename and assignment number. The student is also given the choice of turning in the contents of the main editor window, or a file. In this way, users experienced with the old protocol of turning in a file will be able to use the new interface. The \italic{Grade}, \italic{Handouts} and \italic{Exchange} buttons all pop up a new window that contains a list of papers to select, along with appropriate operations to perform on the selected papers. For example, to annotate a paper turned in by a student, the teacher clicks the \italic{Grade} button and positions the "Papers to Grade" window. Figure 3 shows a typical "Papers to Grade" window: \begindata{raster,272128432} 2 0 58514 58514 0 0 504 254 bits 272128432 504 254 ZZZI | ZZZI | c0zzo+2223 | c0zzo28*888f | c0zzo+2227 | c0zzo28*889f | c0zzo22*aaab | c0zzo29*557f | c0p1ffcr01f8j 0ci0ch30q22*aa 97 | c0p1ffeoc0h07 fej0ci0cg1830 q29*557f | c0p1806oc0h!0f j0ci0cg1830q22 *aaab | c0p1803oc0h1c 03j0ci0cg1830 q29*557f | c0p1803oc0h18 0180i0ci0cg18 30q22*aa97 | c0p180307c0cf g7819c7e003f0 7cg380183387c 03cc0781800cf0 7e3060p29*557f | c0p18030fe0G81 fe1bcff003f0fe g30g0378fe07fc 1fe1800ff87e30 e0p22*aaab | c0p18061c70f1 c38e1f1c38gc1 c7g30g03e1c70e 3c38e1800f1c18 31c0p29*557f | c0p1ffe1830e0 c3031e!18gc183 g30g03c1830c1c !30g0e0c183380 p22*aa97 | c0p1ff8g70c066 031c18hc30180 301fc38007180c 6030g0c061837 q29*557f | c0p18g03f0c066 03181ehc30180 301fc3g3f180c 6030g0c06183e q22*aaab | c0p18g0ff0c067 G180fc0gc30180 30gc3gG180c7f f0g0c06183cq29 *557f | c0p18g1e30c067 G1803f0gc30180 30gc301e3180c 7ff0g0c06183e q22aafab2bf2a 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c8888czzm23*55 57 | c0g04zzm2bR | e22224zzm22*aa ab | c0g04zzm2fR | ZZZI | c0zzzg03 | c0zzzg03 | c0zzzg03 | c7f6l08pc0zzh 03 | c492l18p40zzh 03 | c492l18k08j40 zzh03 | c082c397381c5c e0283638d8e5ce 1e703eb9c3c7zzh 03 | c083644d443235 10481b646d1352 08d8486b264880 zzg03 | c08227c87c0621 f048110c45f218 08884440644f80 zzg03 | c0822408401a21 g88113445020c 08886441a448zzh 03 | c0822408402221 gfc1144450206 088838422448zzh 03 | c0822648643221 90081b646d9212 08d8204326cc80 zzg03 | c1c7739c381d70 e008163a58e71c 06703ce1d327zzh 03 | c0n10g40j42zzk 03 | c0n10g40j66zzk 03 | c0n38ge0j3czzk 03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | ZZZI | ZZZI | \enddata{raster, 272128432} \view{rasterview,272128432,33,0,0} Figure 3: Screen dump of "Papers to Grade" window The teacher clicks on the desired paper and then clicks the \italic{Edit} button. The file is fetched from the \italic{turnin} server into the main editor window of the grade program. The teacher then marks up the document. An object called \italic{note} was developed for annotation. The ATK editor treats the \italic{note} like a large character with internal state. When the \italic{note} is \bold{closed}, it appears as an icon of two little sheets of paper. When \bold{open}, the text of the annotation is displayed. The user clicks on the icon to open the \italic{note}, and on the black region at the top of the \italic{note} to close it. Athena users of the ATK based editors such as \italic{eos}, \italic{grade} and \italic{ez}, get the additional menu commands to create a new \italic{note}, and to open and close all notes. When the teacher is finished modifying the file, he or she clicks the \italic{Return} button, and the file is sent back to the \italic{turnin} server for later \italic{Pick Up} by the student. Figure 4 shows how a file with one open \italic{note}, and two closed \italic{notes} would look in a typical \italic{grade} editor window: \begindata{raster,271271928} 2 0 58514 58514 0 0 504 504 bits 271271928 504 504 ZZZI | ZZZI | e2(2223)2232(22 23)222a(2226(22 23 | c8(888b)88b8(88 8b)8898(888c(88 8f | e2(2225)2252(22 25)221a(2236(22 27 | c8(888f)88f8(88 8f)88f8(88bc(88 9f | e2(aaab2a(aab2 (aaab2a)aa2a'aa ae2a'aaab | c9(555f85(55f8 (555f85(55f8d5 '557c95'557f | e2(aab52a'aaab 52(aab52a(aa5a 2a'aad62a'aa97 | c9(555f85(55f8 (555f85(55f8d5 '557c95'557f | e2(aaab2a(aab2 (aaab2a)aa2a'aa ae2a'aaab | c9(555f85(55f8 (555f85(55f8d5 '557c95'557f | e2(aab52a'aaab 52(aab52a(aa5a 2a'aad62a'aa97 | c9(555f85(55f8 (555f85(55f8d5 '557c95'557f | e2(aaab2a(aab2 (aaab2a)aa2a'aa ae2a'aaab | c9(555f85(55f8 (555f85(55f8d5 '557c95'557f | e2(aab52a'aaab 52(aab52a(aa5a 2a'aad62a'aa97 | c9(555f85(55f8 (555f85(55f8d5 '557c95'557f | e2(aaab2a(aab2 (aaab2a)aa2a'aa ae2a'aaab | c9!555e!5557"55 5f85555f95%55 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c8888czzy03 | e22224zzy03 | c8888czzy03 | e22224zzy03 | c0g04zzy03 | c8888czzy03 | c0g04zzy03 | e22224zzy03 | c0g04zzy03 | c8888czzy03 | c0g04zzy03 | e22224zzy03 | c0g04zzy03 | c8888czzy03 | c0g04zzy03 | ZZZI | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | c0zzzg03 | ZZZI | ZZZI | \enddata{raster, 271271928} \view{rasterview,271271928,34,0,0} Figure 4: Screen dump of active \italic{grade} window Although not shown in these basic demonstration figures, the ATK editor allows formatted text, and a rich variety of other types of data to be put in documents such as equations and line drawings. This capability will be exploited as more real-world documents such as proposals and articles are exchanged for annotation with \italic{turnin}. With the \italic{grade} and \italic{eos} applications, we finally realized the goal of enabling the teacher to point at papers on the screen, view them in final form, annotate them, and return them. The students are able to use the integrated system to receive the annotated papers, and use them directly for their next draft simply by deleting the annotations after reading them. \subsection{3.3 Deployment Strategy } We are following a conservative path for migrating users to the new server. Although the greater maintainability is tempting, our first priority is reliable service. We decided to extensively test and experiment with the new version before getting rid of the old version. Consequently the new server and applications programs have only been in use by two classes of 25 students each for the past term. The single server configuration has been running for 94 days so far without crashing. Nobody has reported a single problem with server reliability. These two courses, however can be considered well behaved. One of the professors had extensive experience with the old \italic{turnin} and never tries anything out of the ordinary. The two courses share the same teaching assistant who also had extensive experience with \italic{turnin}. This summer we plan test \italic{turnin} with simulated work loads of courses with 250 students in them. We hope to offer \italic{turnin} this September as a replacement option for all courses presently using the NFS based \italic{turnin}. Our development team has acquired a reputation for producing good software, so we expect that courses will be strongly encouraged to use the new \italic{turnin}. We hope to phase out the NFS based \italic{turnin} by the end of next academic year. We will verify that our quota management procedures are workable. This will involve discussions with the operations staff to determine if separate volumes should be created or if the server should be changed to set a particular owner, or if it should enforce a quota itself. \section{4 Future directions } The present system allows storing files on secondary servers, identifying when all files are accessible, and merging in files from several places. It still has no provision for dividing work amongst servers in an equitable way. The list of servers to contact, and in what order is either registered with our \italic{Hesiod} name server [Dyer1988] , or set in the \typewriter{FXPATH} environment variable. This makes determining primary and secondary servers a very static process. Since the database is replicated, it should store a mapping of course name to a record of primary server and secondary servers. Then the FX library can contact any server for a list of the appropriate servers. The database can change the servers at any time. We initially expect a person to monitor the usage and adjust the database. In the far future heuristics to do load balancing automatically could be added. We expect the user interface to continue to evolve into smoother integration with classroom procedures. We would like to produce a set of interfaces for industrial use. The user paradigm would be documents cycling between author and either management or peers for review and revision. The command line user interfaces would work, as is, on any UNIX platform that could accommodate a port of the FX library. It is possible that the WYSIWYG integrated interfaces could be ported to other platforms. Since the Andrew Toolkit has window system independent imaging model, a Presentation Manager, or Macintosh Toolbox based system could be produced with only moderate effort. The FX client library could be converted back into a filesystem based back end for use on timesharing hosts, or other transport mechanisms could be used in place of Sun RPC. We started with a simple user interface idea: exchange files as if they were papers passed around in class. We now have a body of knowledge about this application domain, and a body of code that implements several variations on this theme. A variety of interesting extensions can be made at comparatively low cost now that the basic work is done. \section{5 References } \formatnote{.so /usr/lib/tmac/tmac.s .po 1.25i .vs 12 .]< .\\"Barrett.E.-1987-4 .ds [F Barrett1987 .]- .ds [A E. Barrett .as [A ", F. Bequaert .as [A ", and J. Paradis .ds [T Electronic Classroom: Specification for a user interface .ds [D 4 June 1987 .ds [I Athena Writing Project .ds [C Boston, MA .nr [T 0 .nr [A 0 .nr [O 0 .][ 2 book .\\"Camblor.M-1988-5 .ds [F Camblor1988 .]- .ds [A Maria Camblor .as [A ", Rob Shaw .as [A ", Bruce Lewis .as [A ", and William Cattey .ds [T File Exchange For The Educational On-Line System, .ds [T Design Specification .ds [D February 1988 .ds [I Athena Writing Project .ds [C Boston, MA .nr [T 0 .nr [A 0 .nr [O 0 .][ 2 book .\\"DellaFera.C.A-1988-1 .ds [F DellaFera1988 .]- .ds [A C. Anthony DellaFera .ds [T The Zephyr Notification Service .ds [J Proceedings of the USENIX Winter Conference .ds [I USENIX Association .ds [C Berkeley, CA .ds [P 213\\-219 .nr [P 1 .ds [D February, 1988 .nr [T 0 .nr [A 0 .nr [O 0 .][ 1 journal-article .\\"Dyer.S.P.-1988-10 .ds [F Dyer1988 .]- .ds [A Stephen P. 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