- Basic orientation before starting this problem set (read these now)
- Philip and Alex's Guide to Web Publishing, available at http://philip.greenspun.com/panda/, Chapters 1, 4, 5, 10, 11
- Introduction to AOLserver: Part 1 and Part 2
- Information you will need to complete the exercises below (skim
these now and consult them later as necessary)
- SQL for Web nerds, available at http://philip.greenspun.com/sql/, Chapters 1-9
- Tcl for Web Nerds, available at http://philip.greenspun.com/tcl/
Practical Programming in Tcl and Tk (Brent Welch 1997; Prentice-Hall), all the chapters up until the Tk stuff
the Tcl 8.3 man pages
- Brief introduction to database access using AOLServer and the ACS
- Useful references
- AOLserver 3.0 Tcl Developer's Guide
- Common errors by database-backed Web application programmers.
- Complete AOLserver 3.0 Documentation
- Complete Oracle documentation at http://oradoc.photo.net
- Helper and example files ps-basics.tar
Online bboard for assistance: OpenACS Q&A
Objectives: By doing this problem set you will learn:
- How to log into your development server
- Rudiments of Tcl
- How to run Tcl from the shell via tclsh
- How to write simple dynamic web pages using the ADP templating facility of AOLserver
- How to create, execute, test, and debug a .tcl page
- How to write a .tcl page that queries a foreign server
- Rudiments of SQL
- How to query Oracle from the shell using SQL*Plus
- How to write a .tcl page that queries Oracle
- How to personalize Web services by issuing and reading cookies
- How to read and write data in XML
- How to use SQL*Loader
This problem set requires you to learn a lot of new software, so make sure you get started early: plan to spend at least two or three sessions on it. There is nothing difficult here, but you need to work through the initial mechanics of using Tcl, SQL, and running the Web server; and this takes time.
Please feel free to use the on-line forum to ask your questions about this problem set or any other problem. You can use the forum to view other people's questions, and provide or view answers.
Finding your Web server
Check to see that your Web server is running by visiting the address for your server from a Web browser running on your local client machine (not on your Web server machine). If the server is running, you'll see a message with the name of your virtual server, followed by "test page."
Getting Started with Tcl
Exercise 1: Running Tcl from the shell
Run Emacs on your server machine. Type "
m-x shell" to get a Unix shell. Type "
tclsh" to start the Tcl shell program. Try a few simple Tcl commands. Also, type "
info tclversion" at the
tclsh prompt to make sure that you're running Tcl 8.3, the same
version that is compiled into AOLserver.
Using tclsh evaluate 2+2 and (if you feel like being a MIT geek) now define a recursive Fibonacci procedure in Tcl. Execute and test.
Hint: If you're writing Tcl programs of more than two or three lines, you'll find it more convenient to type the code into a separate Emacs buffer (set the buffer to to tcl mode using m-x tcl-mode) and cut and paste from there into the Tcl shell buffer. Actually, you'll almost never be running Tcl from the shell in this course, but you will be writing lots of Tcl in Emacs as you create Web pages.
Exercise 2: Running Tcl from an (almost) HTML page
Look at two-plus-two.adp (source). This is an example of the
ADP (AOLserver Dynamic Page) templating facility in AOLserver. You
can view the source from your web browser, but you should also read it
into an emacs buffer, since you will need to edit it. The
source code should be in the file
If these files are missing from your server machine, download them
from ps-basics.tar and put them in
Augment the page so that (1) you add a $4000 South American Cichlid aquarium as an option, (2) you add an element to the aquarium for how many of each type of aquarium will be installed, and (3) you print out quantity-dependent subtotals and the grand total at the bottom.
Hint: If the code you write doesn't produce what you expect when you
load the page (or, as is common, produces nothing at all), this is
likely to be a Tcl error. To see if there was an error, look at the
error log for your server, which is in the file
Exercise 3: Simple Tcl pages
Using the Web browser running on your local machine, visit the URL
Using Emacs running on the server machine, examine the source code for
this page in
Also look at the source code for the target of the form, which is in
If these files are missing from your server machine, download them
and put them in
Notice how we use Tcl to read the form variables. Try out the form a
couple of times, using your browser. Now debug the regular expression
simple-tcl-page-2.tcl so that it properly handles the
names "Tammy Faye Baker" and "William H. Gates III."
Hint 1: It is easier if you don't try to do this in a single regexp. Use if then elseif then elseif ...
regexp has a side-effect. If you use a
if statement, make sure that you wrap your
regexp in braces so that they don't all get
Hint 3: Keep in mind that a match succeeds if the pattern matches a substring of the data. If you want to force your pattern to match the entire data item, you'll have to use an appropriate regexp to ensure this.
Exercise 4: Tcl pages that query foreign servers
Using the Web browser running on your local machine, visit the URL
http://www.webho.com/WealthClock. Read the discussion of this program
10 of Philip and Alex's Guide to Web Publishing.
Drawing upon that program as a model, build a new web service that
takes the ISBN of a book from a form and then uses
ns_httpget to query several online bookstores to find
price and stock information and displays the results in an HTML table.
Save your program in files called
books-2.tcl so people
can access your service over the web.
We suggest querying barnesandnoble.com and www.1bookstreet.com. Your
program should be robust to timeouts, errors at the foreign sites, and
network problems. You can ensure this by wrapping a Tcl
catch statement around your call to
ns_httpget. Test your program with the following ISBNs:
0385494238, 0062514792, 0140260404, 0679762906.
Try adding more bookstores, but you may need to do kludges to make them work. For example, amazon.com and wordsworth.com tend to respond with a 302 redirect if the client doesn't give them a session ID in the query.
Extra credit: From which of the preceding books is the following quote taken?
This would be a good time to take break.
Getting started with Psql
Start up again with Emacs (you took a break, right?) and start a Tcl shell as before ("M-x shell" then "tclsh"). Type "M-x rename-buffer" to rename the shell to "tcl-shell." Type "M-x shell" to then get a new Unix shell. Rename this buffer "sql-shell." In the SQL shell, type "psql" to start psql, the Postgres shell client. It's convenient to work like this using two shells, one for Tcl and one for SQL.
Exercise 5: Talking to Postgres from the shell
Type the following at psql to create a table for keeping track of the classes you're taking this semester:
create table my_courses ( course_number varchar(20) );
Note that you have to end your SQL commands with a semicolon in psql. These are not part of the SQL language and you shouldn't use these when writing SQL in your Tcl programs for AOLserver.
Insert a few rows, e.g.,
insert into my_courses (course_number) values ('6.916');
Commit your changes:
See what you've got:
select * from my_courses;
One of the main benefits of using an RDBMS is persistence. Everything that you create stays around even after you log out. Normally, that's a good thing, but in this case you probably want to clean up after your experiment:
drop table my_courses;
Quit psql with the
Exercise 6: Tcl pages that talk to Oracle
Look at the file
the source code for a page that displays quotations that have been
stored in the Oracle database. Visit this page with your Web browser
and you should get an error. The reason for the error is that the
program is calling a procedure that doesn't exist:
ad_header ("ArsDigita Header").
You can confirm this suspicion by using
Emacs to read
/home/aol/log/yourvirtualserver-error.log, which is
where AOLserver logs any notices or problems.
To get AOLserver to load procedure definitions at server startup, you
have to put .tcl files in your server's private Tcl library:
/web/yourvirtualserver/tcl/. Create a file called "basics-defs.tcl" in
this directory and define the following Tcl procedures:
ad_header page_title-- returns
bodytags, with argument enclosed within the
ad_footer-- returns a string that will close the
Reload the quotations.tcl page and you get ... the same error!
AOLserver doesn't know that you've added a file to the private
library; this is only checked at server startup. Go to a Unix shell
and "restart-aolserver yourservername" (this is the big hammer; it
kills your server's Unix process so that Unix will restart AOLserver
restart-aolserver does not come back
with "Killing 10234" or some other process ID, you'll know that you
did not succeed (perhaps you made a typo when specifying your server
Reload the quotations.tcl page and you get ... a slightly different
error! The program is trying to query a table that doesn't exist:
Go back to your sql shell and restart SQL*Plus. Copy the table
definition from the comments at the top of the file
feed this definition to Oracle. Go back to your Web browser and
reload the page that previously gave you an error. Things should now
work, although the
quotations table is empty.
Use the form on the web page to manually add the following quotation, under an appropriate category of your choice: "640K ought to be enough for anybody" (Bill Gates). Note that it would be funnier if our table had a column for recording the date of the quotation (1981) but we purposely kept our data model as simple as possible.
Return to SQL*Plus and
select * from the table to see
that your quotation has been inserted into the table. The horrible
formatting is an artifact of your having declared the
quote column to be 4000 characters long.
In SQL*Plus, insert a quotation with some hand-coded SQL. To see the
form of the SQL
insert command you should use, examine
the code on the page quotation_add.tcl. After creating this new table
select * again, and you should now see two rows.
Hint: Don't forget that SQL quotes strings using single quote, not double quote.
Now reload the
quotations.tcl URL from your Web browser.
If you don't see your new quotation here, that's because you didn't type
COMMIT; at SQL*Plus. This is one of the big features of a relational
database management system: simultaneously connected users are
protected from seeing each other's unfinished transactions.
Preloading tables from data files
Now it is time to preload your quotations database with some interesting material, using Oracle's SQL*Loader utility. With Emacs, examine the file
This is a SQL*Loader control file. You'll look at SQL*Loader
more in Oraexercise 1 (below). For now, just invoke SQL*Loader from
the Unix shell with the
sqlldr userid=your-id control=quotation-list.ctl
Here your-id should be your database username followed by a
slash, followed by your database password. Reload the
quotations.tcl web page, and verify that the new
quotations are in the data base. If you check you directory, you
should see that SQL*Loader also generated a
Working with AOLserver and Oracle
Study the source code for the pages
quotation-add.tcl, paying particular attention to how they
access the database. Notice how they represent SQL commands as
strings in Tcl, which are then used together with appropriate Tcl
commands from the database API. You can find some documentation on
the API in Brief
introduction to database access using AOLServer and the ACS, but
the comments in the code files should be reasonably self-explanatory.
Exercise 7: Improving the User Interface for data entry
Go back to the main
quotations.tcl page and modify it so
that the categories entry is done via a select box of existing categories
(you will want to use the "SELECT DISTINCT" SQL command). For new
categories, provide an alternative text entry box labeled "new
category." Make sure to modify
quotation-add.tcl so that
it recognizes when a new category is being defined.
Hint: In order to simplify debugging, you may find it useful to test your query using SQL*PLUS in the shell, before integrating the query into a Tcl page.
Exercise 8: Searching
Add a small form at the top of quotations.tcl that takes a single query word from the user. Build a target for this form that returns all quotes containing the specified word. Your search should be case-insensitive and also look through the authors' column.
Hint 1: Read about simple queries in SQL for Web nerds.
Hint 3: SQL's UPPER and LOWER functions
Personalizing Web services with cookies
We'd like you to build a system that implements per-user personalization of the quotation database. The overall goal should be
- A user can "kill" a quotation and have it never show up again either from the top-level page or the search page.
- Killing a quotation is persistent and survives the quitting and restarting of a browser.
- Quotations killed by one user have no effect on what is seen by other users.
- Users can erase their personalizations and see the complete quotation database again by clicking on an "erase my personalization" link on the main page. This link should appear only if the user has personalized the quotation database.
You can personalize Web services with the aid of magic cookies. A cookie issued by the server directs the browser to store data in the browser's computer. To issue a cookie, the server includes a line like
Set-Cookie: cookie_name=value; path=/ ; expires=Fri, 01-Jan-2010 01:00:00 GMT
in the HTTP header sent to the browser. Here
cookie_name is the
name for this cookie, and
value is the associated value,
which can contain any character or format except for semicolon, which
terminates a cookie. The
path specifies which URLs on
the server the cookie applies to. Designating a path of
/) includes all URLs on the server.
After the browser has accepted a server's cookie, it will include the cookie name and value as part of its HTTP requests whenever it asks that server for an applicable URL. Your Tcl programs can read this information using the AOLServer API
[ns_set get [ns_conn headers] Cookie]
After the expiration date, the browser no longer sends the cookie information. The server can also issue cookies with no specified expiration date, in which case, the cookie is not persistent -- the browser uses it only for that one session.
You can see an example of how cookies are issued and read, by
visiting the URL
and examining the Tcl for file and the associated URLs
Observe how expire-cookies gets rid of cookies by reissuing them with
an expiration date that has already past.
Reference: The magic cookie spec is available from http://home.netscape.com/newsref/std/cookie_spec.html.
Implement the personalized quotation system described above.
Hint 1: It is possible to build this system using an ID cookie for the browser and keeping the set of killed quotations in Oracle. However, if you're not going to allow users to log in and claim their profile, there really isn't much point in keeping data on the server. In fact, by keeping killed quotation IDs in your users' browser cookies, you've achieved the holy grail of academic database management system researchers: a distributed database!
Hint 2: It isn't strictly copacetic with the cookie spec, but you can have a cookie value containing spaces. Tcl stores a list of integers internally as those numbers separated by spaces. So the easiest and simplest way to store the killed quotations is as a space-separated list.
Hint 3: Don't filter the quotations in Tcl. It is generally a sign of incompetent programming when you query more data from Oracle than you're going to display to the end-user. SQL is a very powerful query language. You can use the NOT IN feature to exclude a list of quotations.
How about taking another break?
Sharing data with XML
As you learned above from querying bookstores, data on the Web has not traditionally been formatted for convenient use by computer programs. The bookstore program you wrote could easily break if Barnes and Noble changed the formatting of its web page to indicate the book price in some other way.
In theory, people who wish to exchange structured data over the Web can cooperate using XML (eXtensible Markup Language), a 1998 standard from the Web Consortium (www.w3.org/XML/). XML has started to become widely hyped over the past year as "the next big thing on the Web," but in practice, hardly anybody uses XML yet (summer 2000). Fortunately for you in completing this problem set, you can cooperate with your fellow students: the overall goal is to make quotations in your database exportable in a structured format so that other students' applications can read them.
In order to cooperate, we need (1) an agreed-upon URL at everyone's server where the quotations database may be obtained; and (2) an agreed-upon format for the quotations. In point of fact, we could avoid the need for prior agreement by setting up infrastructures for service discovery and by employing techniques for self-describing data -- both of which we'll deal with later in the semester -- but we'll keep things simple for now.
We'll format our quotations using XML. XML structures consist of data
strings enclosed in HTML-like tags of the form
what kind of thing the data is supposed to be.
Here's an informal example, showing the structure we'll use for our quotations:
1 1999-02-04 Bill Gates Computer Industry Punditry640K ought to be enough for anybody. .. another row from the quotations table ...... some more rows
Notice that there's a separate tag for each column in our SQL table:
There's also a "wrapper" tag that identifies each row as a
structure, and an outer wrapper that
identifies a sequence of
structures as a
Building a DTD
We can give a formal description of our XML structure, rather than an informal example, by means of an XML Document Type Definition (DTD).
Our DTD will start with a definition of the
ELEMENT quotations (onequote)+
This says that the
quotations element must contain at
least one occurrence of
onequote but may contain more
than one. Now we have to say what constitutes a legal
ELEMENT onequote (quotation_id,insertion_date,author_name,category,quote)
This says that the sub-elements, such as
each appear exactly once and in the specified order. Now we have to
define an XML element that actually contains something other than
other XML elements:
ELEMENT quotation_id (#PCDATA)
This says that whatever falls between
is to be interpreted as raw
characters rather than as containing further tags (PCDATA stands for
"parsed character data").
Here's our complete DTD:
ELEMENT quotations (onequote)+ ELEMENT onequote (quotation_id,insertion_date,author_name,category,quote) ELEMENT quotation_id (#PCDATA) ELEMENT insertion_date (#PCDATA) ELEMENT author_name (#PCDATA) ELEMENT category (#PCDATA) ELEMENT quote (#PCDATA)
The point of building a DTD is not just to satisfy some anal, formalistic craving of Web protocol designers. Rather, the DTD provides a machine-readable description of the XML data structure that can be fed to parsers that can then automatically tokenize the XML document. (This is a simple example of a self-describing data technique.)
In this problem set; however, we won't use the DTD at all. You'll
need to use only the informal XML
Exercise 10: Generating XML
Tcl program that queries the
quotations table, produces an XML document in the
preceding form, and returns it to the client with a MIME type of
"application/xml." Place this in a file quotations-xml.tcl, so that
other users can retrieve the data by visiting that agreed upon URL.
To get you started, we've provided the file
Requesting this URL with a Web browser should offer to let you to save
the document to a local file, and you can then examine it with a text
editor on your local machine. (Alternatively, your browser may
already have some special behavior defined for MIME type application/xml. IE
5.5, for example, will automatically display the XML document.) The
differences between our example and your program is that you'll need
to produce a document containing the entire table and you'll need to
generate it on the fly.
Exercise 11: Importing XML
Write a program to import the quotations from another student's XML output page (if you have completed the previous exercise and your peers have not, this might be a good time to exhort them to greater efforts). Your program must
/psets/basics/quotations-xml.tclfrom another student's server using
- Parse the resulting XML structure into records and the parse the records into fields.
- If a quote from the foreign server has identical author and
content as a quote in your own database, ignore it; otherwise, insert
it into your database with a new
quotation_id. (You don't want keys from the foreign server conflicting with what is already in your database.)
Hints: You might want to set up a temporary table using
table quotations_temp as select * from quotations and then drop
it after you're done debugging, so that you don't mess up your own
Rather than having you work with DTDs and general XML parsers, we've
gone for simplicity here by predefining for you a parser in Tcl that
understands only this particular quotations XML structure. The
procedure is parse-all.tcl.
You have to install this file in your server's private Tcl library,
/web/yourvirtualserver/tcl/, for this function
to be callable by .tcl and .adp pages. (Don't forget to restart your
Web server.) The
parse_all procedure takes an XML
quotation structure as argument and returns a Tcl list, showing the
parts and subparts of the structure. To see an example of the format,
use your browser to visit the page
Note: these exercises are designed to familiarize you with XML. In
most cases, XML processing should be done using Oracle's Java
Exercise 12: Tracking a book's popularity
Neurotic authors will constantly check amazon.com to see where their book is ranked in terms of sales. That these figures are updated hourly only makes the habit more destructive. Write a program to track a very neurotic author's work (ISBN 1558605347). You will need to
- define an Oracle table to hold ISBN, date-time, sales rank;
- write a procedure that will grab the Amazon page, REGEXP out the sales rank, and stuff it into the Oracle table;
- use the AOLserver API call
ns_schedule_procto schedule your procedure to run once every hour;
- build a .tcl page to look at the popularity over time.
One of the interesting things about Amazon is that they often lose control of their server farm and database (they write a lot of C code and one programmer's sloppiness can generate a catastrophic failure of the entire service). You might want to build your system so that you can record (a) times when amazon.com is unreachable, and (b) for which of those times the page served contains the string "Our store is closed temporarily for scheduled maintenance" (you'll sometimes get this during the middle of weekdays when they would definitely not have intentionally scheduled any maintenance).
Exercise 13: Becoming a chartoonist
Why print a table of a book's popularity when you can print a chart? You're going to learn about the wonders of single-pixel GIFs and WIDTH and HEIGHT tags now. Grab the software in http://web.archive.org/web/20010225175647/http://software.arsdigita.com/tcl/ad-graphing.tcl and put it in your server's private Tcl directory (/web/yourservername/tcl/). Read the docs at http://web.archive.org/web/20010309075833/http://software.arsdigita.com/www/doc/graphing.html and then write code to generate a pretty chart of the data from Exercise 12.
Note that you're dipping into the ArsDigita Community System toolkit here, the software with which you'll be occupied in Problem Set 2.
The Wide World of Oracle
We're now going to shift gears into a portion of the problem set designed to teach you more about Oracle and SQL.
Oraexercise 1: SQL*Loader
- Use Emacs to create a list of five records, each record containing a stock symbol, an integer number of shares owned, and a date acquired (in the form MM/DD/YYYY)
- Create a SQL table to hold these data:
create table my_stocks ( symbol varchar(20) not null, n_shares integer not null, date_acquired date not null );
- Use SQL*Loader to preload your data into the
my_stockstable. You'll have to create an appropriate control file, as when you earlier preloaded the quotations table. You can probably guess the format of the control file by analogy with the quotations example, but you should at least be aware of the existence of the SQL*Loader documentation in the Oracle docs at http://philip.greenspun.com/sql/ref/utilities)
Hint: If you leave blank lines at the end of the control file, the log file will contain error complaints about bad records with missing columns, since Oracle's implementation is too shoddily written to realize that a blank line isn't supposed to be a record definition. (What can you expect from a company with a mere $10 billion in annual revenues?)
Oraexercise 2: Copying data from one table to another
This exercise exists because we found that, when faced with the task of moving data from one table to another, people were dragging the data from Oracle into AOLserver, manipulating it in Tcl, then pushing it back into Oracle. This is not the way! SQL is a very powerful language and there is no need to bring in any other tools if what you want to do is move data around within Oracle.
- Using only one SQL statement, create a table called
stock_priceswith three columns:
symbol, quote_date, price. After this one statement, you should have created the table and filled it with one row per symbol in
my_stocks. The date and price columns should be filled with the current date and a nominal price.
Select symbol, sysdate as quote_date, 31.415 as price from my_stocks;.
- Create a new table:
create table newly_acquired_stocks ( symbol varchar(20) not null, n_shares integer not null, date_acquired date not null );
- Using a single
insert into .. select ...statement (with a WHERE clause appropriate to your sample data), copy about half the rows from
Oraexercise 3: JOIN
With a single SQL statement JOINing
stock_prices, produce a report showing symbol, number of
shares, price per share, and current value.
Oraexercise 4: OUTER JOIN
Insert a row into
my_stocks. Run your query from
Oraexercise 3. Notice that your new stock does not appear in the
report. This is because you've JOINed them with the constraint that
the symbol appear in both tables.
Modify your statement to use an OUTER JOIN instead so that you'll get a complete report of all your stocks, but won't get price information if none is available.
Oraexercise 5: PL/SQL Functions and Packages
Inspired by Wall Street's methods for valuing Internet companies, we've developed our own valuation method for this problem set: a stock is valued at the sum of the ascii characters making up its symbol. (Note that students who've used lowercase letters to represent symbols will have higher-valued portfolios than those will all-uppercase symbols; "IBM" is worth only $216 whereas "ibm" is worth $312!)
- define a PL/SQL function that takes a trading symbol as
its argument and returns the stock value (hint: Oracle's built-in
ASCIIfunction will be helpful);
- with a single UPDATE statement, update
stock_pricesto set each stock's value to whatever is returned by this PL/SQL procedure;
- define a PL/SQL function that takes no arguments and returns the
aggregate value of the portfolio (
n_shares * pricefor each stock). You'll want to define your JOIN from Oraexercise 3 (above) as a cursor and then use the PL/SQL Cursor FOR LOOP facility. Hint: when you're all done, you can run this procedure from SQL*Plus with
select portfolio_value() from dual;.
In addition to
functions, PL/SQL offers another type of block called
packages. You can read the refrence material about PL/SQL packages at http://web.archive.org/web/20020910135006/http://oradoc.photo.net/ora816/appdev.816/a77069/08_packs.htm Packages provide a powerful resource for extending the laguage and increasing maintainablity by storing related objects together. A package has two parts: the
header is a declarative section providing specifications for the procedures/functions and the
body that contains code for the procedures defined in the header.
You should create a package
stockpack.sql and modify your code to incorporate the package calls for the procedures. Remember that the package
header has to be compiled before the
body can be compiled successfully in your
Oraexercise 6: Buy more of the winners
Rather than taking your profits on the winners, buy more of them!
- use SELECT AVG() to figure out the average price of your holdings;
- Using a single INSERT with SELECT statement, double your holdings
in all the stocks whose price is higher than average (with
Rerun your query from Oraexercise 4. Note that in some cases you will have two rows for the same symbol. If what you're really interested in is your current position, you want a report with at most one row per symbol.
- use a SELECT ... GROUP BY query from
my_stocksto produce a report of symbols and total shares held;
- use a SELECT .. GROUP BY query JOINing with
stock_pricesto produce a report of symbols and total value held per symbol;
- use a SELECT .. GROUP BY .. HAVING query to produce a report of symbols, total shares held, and total value held per symbol restricted to symbols in which you have at least two blocks of shares (i.e., the "winners").
Oraexercise 7: encapsulate your queries with a view
Using the final query above, create a view called
stocks_i_like that encapsulates the final query.
Information Architecture and User Interface
You've got a database table filled with stock data. There are a couple of ways to provide a Web interface to these data. The loser Web developer presents a page with options for retrieving stock data:
- show recent acquisitions
- show best performers
- show highest value stocks
- show entire portfolio
The bottom line is that the user doesn't see anything on the first page. From an information presentation point of view, the first page is therefore a waste.
An alternative is to show the user a table of holdings right on the top-level page, with a sensible subset of the data by default, and provide controls to adjust what is included in the display. What kind of controls? You could have the ones above, plus whatever other views the publisher of the site and the users eventually decide are necessary. Suppose, though, that you can organize the controls along orthogonal dimensions. If you can do that, with just a handful of "dimensional sliders," the user will have many options.
For example, the ArsDigita ticket tracking system is used to store bug reports and feature requests. The following dimensions are employed
- involvement of connected user (values: mine/everyone's)
- ticket status (values: open/+deferred/+closed)
- ticket age (values: last day/last week/last month/all)
Note that even though these are modeled as continuous dimensions, the user is not presented with continuous sliders. The user picks one of several discrete points on each dimension. This interface is compatible with the Netscape 1.1 browser and provides the user with 24 choices in total. Yet instead of seeing 24 options in a big list, the user sees one line across the top of the browser, with nine buttons arranged logically into three dimensions.
If those 24 options aren't enough, the ticket tracking system lets the user re-sort the table by any of the columns by clicking on the column heading.
Try building the same sort of thing for your stock portfolio. You
want a .tcl page that shows the contents of
stock_prices. Provide controls across the top
(hint: TABLE WIDTH=100% and TD ALIGN=RIGHT will be useful) for the
- recency of acquistions (within last week/last month/last year/all)
- value of holding (more than 10% of total portfolio/more than 2%/all)
Provide the ability for users to sort by any of the columns presented
$SERVER_HOME/tcl/00-ad-utilities.tcl will be useful for this,
notably because of the
exclusion_list argument), e.g.,
symbol, number of shares, price per share, value of holding.
You can build this from scratch or use the OpenACS toolkit API call for ad_table as a building block.
Turning in your work
We expect you to have your code working and debugged before the beginning of the class when it is due. In class, we will use a web browser to connect to several student servers and all look together at the pages, to see how well they work. Also, starting immediately after class, we will examine the contents of your Web server to look at your answers. On Thursday night, you will be required to do a code review with a TA in the lab.
Who Wrote This and When
This problem set was written by Philip Greenspun and Hal Abelson in January 1999 for MIT Course 6.916. It was revised in January 2000 for AOLserver 3.0, which incorporates Tcl 8.3, and revised again in August 2000, with help from Dan Parker, Andrew Grumet, and Ravi Jasuja.
This material is copyright 1999, 2000, by Philip Greenspun and Hal Abelson. It may be copied, reused, and modified, provided credit is given to the original authors with a hyperlink to the original document.
Changes/Suggestions (2002): Carl R. Blesius