A Seamless Model and Language Stephen W. Liddle Brigham Young University

A Seamless Model and Language

Stephen W. Liddle

Brigham Young University

19 June 2001 IWWOST’01, Valencia, Spain – Steve Liddle 2

Outline

Status of implementation Historical perspective Model-equivalent language


In the Beginning

Vannevar Bush, As We May Think, proposed the “memex” in 1945

Then we had hypertext systems HyperCard on the Macintosh was

popular


Then Came the Web

The World Wide Web was enabled by two very simple protocols– HTTP (get, post, …)– HTML (head, body, title, strong, …)

Sites started as fairly simple repositories of pages

Structure was basic: sections, paragraphs, lists, tables, anchors, links, images

Key simplification: no annotation


Then Came Version 2.0

And beyond… Applets, cookies, Cascaded Style

Sheets, XML, JavaScript, server-side includes, server-side scripting, …

Trend to more power, complexity How to we manage complexity?

– Abstraction (modeling)


The History of Semantic Data Models NIAM and ER in the mid 1970’s For more than a decade, extensions

proliferated People learned that too much notation

got in the way, and data models tended to simpler concepts


The History of OO Models

Built on semantic data models and software engineering methods

By the early 90’s were proliferating just like the semantic data models had

“Method Wars” The negotiated peace settlement: UML

– Clearly is a compromise– Too much notation (my opinion)


Sustaining vs. Disruptive Technology Trajectories

Pro

duct

Perf

orm

ance

Time

Progress from

disruptiv

e tech

nologies

Performance demanded by market

Disruptiveinnovation

Progress from

sustaining tech

nologies

Low end

High end


Our Experience with OSM

Work began in the late 80’s Book on Object-Oriented Systems

Analysis (OSA) in the early 90’s Since then our research has generally

used this model as its core


Guiding Philosophy

Take an “ontological” perspective– See Yair Wand’s work, for example

Take a “model-driven” approach– Agnostic toward the methodology– Instead emphasize clarity and purity of the

modeling concepts Provide clear formal definitions


OSM Layers

OSA (analysis) OSS (specification) OSD (design) OSI (implementation) OSE (evolution) All together we call this Object-oriented

Systems Modeling, or OSM


My Task: Implementation

OSA was a nice start Did not provide a clean path to an

implemented system, just to a naturally described system

Did cleanly separate analysis from design features

OSS, OSD, and OSI needed few changes to the basic model in OSA

We called our central model OSM and viewed OSA/OSS/OSD/OSI as shifts in perspective


The State of Software Development Then… Difficult and lossy transformations

between models, languages, tools Inhibited communications (differing

assumptions, definitions) Barriers to seamless tool development Multiple paradigms leading to

complexity and lack of comprehensibility


Has Anything Changed?

Only slightly We do emphasize “standards” now


Inherent Complexity

Software development is innately complex because of:– Sheer size of application– Number of users– Variety/complexity of I/O mechanisms– Originality of innovations created for a

particular system– Sophistication of algorithms required to

address system tasks


Artificial Complexity Software development is artificially (and

needlessly) complex because:– We do not have sufficient abstractions in

• Operating systems• Languages• Models• Other tools

– Ad-hoc mixture of abstractions in our models, languages, tools is poorly integrated, poorly defined, redundant, and inconsistent

We still have lossy transformations The Web has only made it worse


Typical Web Application

Web (HTTP)server

server-sidescript handler

database server

Web browser

client-sidescript handler

rendering engine

Architectural Elements of a Typical Web Application.

<?php @$conn = mysql_pconnect("localhost", "userid", "passwd"); @mysql_select_db("my_database", $conn);

if (!empty($UserID) && !empty($Password)) { $sql = "SELECT * FROM Person WHERE UserID='$UserID' AND " . "Password=PASSWORD('$Password')"; $result = mysql_query($sql, $conn); if ($result) { include("main_menu.php"); exit; } }?><HTML><HEAD> <TITLE>Sample Login Page</TITLE> <STYLE TYPE="text/css"> BODY, P, TD, TH { font-family: arial, geneva, helvetica, sans-serif; font-size: 10pt; } TH { text-align: left; } H1 { text-align: center; font-size: 18pt; } H2 { text-align: center; font-size: 14pt; } </STYLE> <SCRIPT LANGUAGE="JavaScript">  </SCRIPT></HEAD>

PHPScript

StyleSheet

JavaScript

Typical Web Page

<BODY> <H1 ALIGN="CENTER">Please Log In</H1> <FORM NAME="frmLogin" METHOD="POST" ACTION="login.php"> <TABLE BORDER=0 ALIGN="CENTER"> <TR><TH>User ID:</TH> <TD><INPUT TYPE="TEXT" NAME="UserID" VALUE="<?= $UserID ?>" SIZE=15 ONBLUR="trim(this)"></TD> </TR> <TR><TH>Password:</TH> <TD><INPUT TYPE="PASSWORD" NAME="Password" SIZE=15></TD> </TR> <TR><TD COLSPAN=2 ALIGN="CENTER"><INPUT TYPE="SUBMIT" VALUE="Log In"></TD> </TR> </TABLE> </FORM> <HR> Page generated <?= date("d M Y H:i") ?></BODY></HTML>

HTML Form

PHP script writes the current value of $UserID into the text box.

PHP script writes the current date and time to the output page.

When executed on the server, if the user ID and password are found in the database, loads main_menu.php instead of continuing to execute this page.

JavaScript trim function is invoked in the browser when the UserID text box loses the focus. (Removes leading/trailing blanks.)


OSM Is Seamless Single modeling and

development environment Resolves impedance

mismatches:– Structural/behavioral– Imperative/declarative– Visual/textual

Reifies abstract objects– Accessible, formal metamodel– First-class high-level elements

Object Set

Person

P1 P2 P3


Model Equivalent Language

The semantics of the model and language are one-to-one

Programming is merely a shift in perspective to focus on efficient algorithms and structures

A “program” is simply an alternative view of a “model”

“Iteration” is quite simple


Why OSM Is Suitable Foundation Highly expressive Computationally complete Formally defined (with so-called tunable

formalism that allows varying levels of formality and completion)

Provides many different kinds of views


Organization of OSM

Object-Relationship Model– ORM describes structure (summary)

Object-Behavior Model– State nets describe object behavior (summary)

Object-Interaction Model– Interaction diagrams show how objects interact

(synchronize and communicate) (summary) Emphasis on fully reified high-level constructs

(views)


Harmony, the OSM Language

Fully textual version of graphical OSM– Both have same underlying formal

foundation Adds convenient syntactic features

– In the same way graphical models add convenient notations

Examples:– Figures A, B, C


Our Model/Language Features

Multiple paradigms– Declarative, imperative

Nested transactions “Variable” has set semantics, not scalar Type-complete persistence No impedance mismatches


BUT…

No commercial-quality implementation


Proposal for Web Application Modeling Begin with a core conceptual model that is

formal, executable– Ideally, it would have a model-equivalent language

behind it

Need to add navigation and presentation (interface) layers

Use “frameworks” and “architectures” in the sense of design patterns and subsystems


Adhere to Guiding Principles

Ontological perspective Model-driven, not method-driven Clear, formal definitions


Open Problems

Identification of sufficient, concise set of Web application modeling constructs

Complete, formal, ontological semantics for our chosen Web application model– What is navigation, really?

Comprehensive tools to tackle all aspects without introducing lossy transformations

Tools that are good enough to take care of performance tuning issues– No more database administrators?


References

Embley’s OSA and OODB Design books

CRC Press Handbook of Object Technology

Papers linked to the IWWOST Web site http://osm.cs.byu.edu

Documents

A Seamless Model and Language Stephen W. Liddle Brigham Young University