Peter J. Denning (1942) is an American computer scientist, and prolific writer. He is best known for inventing the working-set model for program behavior, which defeated thrashing in operating systems and became the reference standard for all memory management policies. He is also known for his works on principles of operating systems, operational analysis of queueing network systems, design and implementation of CSNET, ACM digital library, and codifying the fundamental principles of computing.

Biography

Denning was born January 6, 1942, in Queens, NY, and raised in Darien, CT. He took an early interest in science, pursuing astronomy, botany, radio, and electronics while in grade school. At Fairfield Prep, he submitted home designed computers to the science fair in 1958, 1959, and 1960. The second computer, which solved linear equations using pinball machine parts, won the grand prize.^[1] He attended Manhattan College for a Bachelor in EE (1964) and then MIT for a PhD (1968). At MIT he was part of Project MAC and contributed to the design of Multics. His PhD thesis, “Resource allocation in multiprocess computer systems”, introduced seminal ideas in working sets, locality, thrashing, and system balance.

At Princeton University from 1968 to 1972, he wrote his classic book, Operating Systems Principles, with E G Coffman. He collaborated with Alfred Aho and Jeffrey Ullman on optimality proofs for paging algorithms and on a simple proof that compilers based on precedence parsing do not need to backtrack. At Purdue University (1972-1983) he supervised numerous PhD theses validating locality-based theories of memory management and extending the new mathematics of operational analysis of queueing networks. He co-founded CSNET. He became department head in 1979. He completed another book on computational models, Machines, Languages, and Computation, with Jack Dennis and Joe Qualitz.

At NASA Ames from 1983 to 1991 he founded the Research Institute for Advanced Computer Science (RIACS)^[2] and turned it into one of the first centers for interdisciplinary research in computational and space science.

At George Mason University from 1991 to 2002 he headed the Computer Science Department, was an associate dean and vice provost, and founded the Center for the New Engineer. The Center was a pioneer in web-based learning. He created a design course for engineers, called Sense 21, which was the basis of his project to understand innovation as a skill. He created a course on Core of Information, Technology^[3] the basis his Great Principles of Computing project.^[4]

At Naval Postgraduate School since 2002 he heads the Computer Science Department, directs the Cebrowski Institute for Innovation and Information Superiority,^[5] and chairs the faculty council.

Denning served continuously as a volunteer in Association for Computing Machinery (ACM) since 1967. In that time he served as president, vice president, three board chairs, Member-at-Large, Editor of ACM Computing Surveys, and Editor of the monthly Communications. He received six ACM awards for service, technical contribution, and education. ACM presented him with a special award^[6] in June 2007 recognizing 40 years of continuous service.

Denning has received 24 awards for service and technical contribution. These include one quality customer service award, three professional society fellowships, three honorary degrees, five awards for technical contribution, six for distinguished service, and six for education.^[7]

He married Dorothy E. Denning in 1974. She went on to become a noted computer security expert.

[edit] Work

Denning’s career has been a search for fundamental principles in subfields of computing. He writes prolifically. From 1980 to 1982 he wrote 24 columns as ACM President, focusing on technical and political issues of the field. From 1985 to 1993 he wrote 47 columns on “The Science of Computing” for American Scientist magazine,^[8] focusing on scientific principles from across the field. Beginning in 2001 he has written 22 “IT Profession” columns^[9] for Communications of the ACM, focusing on principles of value to practicing professionals.

[edit] Virtual memory

In 1970 he published a classic paper that displayed a scientific framework for virtual memory and the validating scientific evidence, putting to rest a controversy over virtual memory stability and performance.^[10]

In 1966 he proposed the working set as a dynamic measure of memory demand and explained why it worked using the locality idea introduced by Les Belady of IBM. His working set paper^[11] became a classic. It received an ACM Best paper award in 1968 and a SIGOPS Hall of Fame Award ^[12] in 2005.

[edit] Operating system principles

In the early 1970s he collaborated with Ed Coffman, Jr., on Operating Systems Theory, which became a classic textbook used in graduate courses and stayed in print until 1995. That book helped to erase doubts that the OS field could be approached as a science.

In the middle 1970s he collaborated with Jeffrey Buzen on operational analysis, extending Buzen’s basic laws to deal with all queueing networks. The operational framework explained why computer performance models work so well, even though violating the traditional stochastic Markovian assumptions. It has become the preferred method for teaching performance prediction in computing courses.

In the early 1980s, he was one of the four founding Principal investigators of Computer Science Network, sponsored by the National Science Foundation The other three were Dave Farber, Larry Landweber, and Tony Hearn. They led the development of a fully self supporting CS community network that by 1986 included 165 sites and 50,000 users. CSNET was the key transitional stepping stone from the original ARPANET to the NSFNET and then the Internet.

He led the Digital Library project 1992-97, which went live in 1997. The Association for Computing Machinery became the first professional society to offer a fully searchable library of everything it ever published.^[13]

[edit] Great Principles of Computing

Denning’s career has been a search for fundamental principles in subfields of computing. In 1999, he expanded the search to cover all of computing. The discovery of natural information processes in biology, physics, economics, materials, and other fields convinced him that the basic definitions of computation had to be modified to encompass both natural and artificial information processes. He and his team have produced a draft framework.^[14]

The Great Principles framework revealed that “innovating” is a core practice of computing. Unable to find anyone who understood how to teach the skill of innovating, he joined with Bob Dunham and identified eight foundational practices of innovation.^[15]

[edit] Computing education

Denning has been a major influence in computing education.^{[citation needed]} In the early 1970s he led a task force that designed the first core course on operating systems (OS) principles. OS became the first non-math CS core course. In the mid 1980s he led a joint ACM/IEEE committee that described computing as a discipline with nine functional areas and three cognitive processes, the basis of ACM Curriculum 1991. In the 1990s he set out on a quest to codify the great principles of computing. He maintains that computing is a science both of natural and artificial information processes. NSF designated him a Distinguished Education Fellow^[16] in 2007 to launch a movement to use the Great Principles framework for innovations in education and research.

Quotes

• Computation is the principle; the computer is the tool.
• All speech is free. It’s just the consequences that get you.
• A request is not in the words you speak. It is in the listening of those who hear you.
• After many years of trying to make computers think like brains, AI researchers got brains that think they are computers.
• Locality is a principle of nature. Caching works because our brains organize information by localities.
• Innovation is not brilliant new ideas; it is new practice adopted by a community.
• Solidarity, not software, generates collaboration.

Network Topology: It is graphical mapping of the configuration of physical and logical connections between nodes. LAN Network Topology is, therefore, technically a part of graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical.

Classification of network topologies

There are also three basic categories of network topologies:

• physical topologies

• signal topologies

• logical topologies

Physical topologies

The mapping of the nodes of a network and the physical connections between them – i.e., the layout of wiring,cables, the locations of nodes, and the interconnections between the nodes and the cabling or wiring system.

Classification of physical topologies

Point-to-point

The simplest topology is a permanent link between two endpoints. Switched point-to-point topologies are the basic model of conventional telephony. The value of a permanent point-to-point network is the value of guaranteed, or nearly so, communications between the two endpoints.

Permanent (dedicated)

Easiest to understand, of the variations of point-to-point topology, is a point-to-point communications channel that appears, to the user, to be permanently associated with the two endpoints.

Switched:

Using circuit-switching or packet-switching technologies, a point-to-point circuit can be set up dynamically, and dropped when no longer needed.

Bus

Linear bus

The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has exactly two endpoints (this is the ‘bus’, which is also commonly referred to as the backbone or trunk)

All data that is transmitted between nodes in the network is transmitted over this common transmission medium and is able to be received by all nodes in the network virtually simultaneously.

Distributed bus

The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has more than two endpoints that are created by adding branches to the main section of the transmission medium – the physical distributed bus topology functions in exactly the same fashion as the physical linear bus topology.

Star

The type of network topology in which each of the nodes of the network is connected to a central node with a point-to-point link in a ‘hub’ .All data that is transmitted between nodes in the network is transmitted to this central node, which is usually some type of device that then retransmits the data to some or all of the other nodes in the network.

Extended star

A type of network topology in which a network that is based upon the physical star topology has one or more repeaters between the central node (the ‘hub’ of the star) and the other nodes, the repeaters being used to extend the maximum transmission distance of the point-to-point links between the central node and the peripheral nodes .

Ring

The type of network topology in which each of the nodes of the network is connected to two other nodes in the network and with the first and last nodes being connected to each other, forming a ring – all data that is transmitted between nodes in the network travels from one node to the next node in a circular manner and the data generally flows in a single direction only.

Mesh

Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. In a ring, although two cable paths exist, messages can only travel in one direction. Some WANs, most notably the Internet, employ mesh routing.

Full

Fully connected

The type of network topology in which each of the nodes of the network is connected to each of the other nodes in the network with a point-to-point link – this makes it possible for data to be simultaneously transmitted from any single node to all of the other nodes.

The physical fully connected mesh topology is generally too costly and complex for practical networks, although the topology is used when there are only a small number of nodes to be interconnected.

Partial

Partially connected

The type of network topology in which some of the nodes of the network are connected to more than one other node in the network with a point-to-point link – this makes it possible to take advantage of some of the redundancy that is provided by a physical fully connected mesh topology without the expense and complexity required for a connection between every node in the network.

Tree

Also known as a hierarchical network.

The type of network topology in which a central ‘root’ node i.e. the top level of the hierarchy is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level) with a point-to-point link between each of the second level nodes and the top level central ‘root’ node, while each of the second level nodes that are connected to the top level central ‘root’ node will also have one or more other nodes that are one level lower in the hierarchy (i.e., the third level) connected to it, also with a point-to-point link, the top level central ‘root’ node being the only node that has no other node above it in the hierarchy Each node in the network having a specific fixed number, of nodes connected to it at the next lower level in the hierarchy, the number, being referred to as the ‘branching factor’ of the hierarchical tree.

Hybrid network topologies

It is combination of different topologies such as star bus topology, star of star, star wired ring, hybrid mesh.

Star-bus

A type of network topology in which the central nodes of one or more individual networks that are based upon the physical star topology are connected together using a common ‘bus’ network whose physical topology is based upon the physical linear bus topology.

Star-of-stars

Hierarchical star

A type of network topology that is composed of an interconnection of individual networks that are based upon the physical star topology connected together in a hierarchical way to form a more complex network .

Star-wired ring

A type of hybrid physical network topology that is a combination of the physical star topology and the physical ring topology.

Hybrid mesh

A type of hybrid physical network topology that is a combination of the physical partially connected topology and one or more other physical topologies the mesh portion of the topology consisting of alternate connections between some of the nodes in the network .

Signal topology

The mapping of the actual connections between the nodes of a network, as evidenced by the path that the signals take when propagating between the nodes.

Logical topology

The mapping of the connections between the nodes of a network, as evidenced by the path that data appears to take when traveling between the nodes.

Classification of logical topologies

The logical classification of network topologies generally follows the same classifications as those in the physical classifications of network topologies, the path that the data takes between nodes being used to determine the topology as opposed to the actual physical connections being used to determine the topology.

1.) Logical topologies are often closely associated with media access control (MAC) methods and protocols.

2.) The logical topologies are generally determined by network protocols as opposed to being determined by the physical layout of cables, wires, and network devices or the logical flow of data.

3.) Logical topologies are able to be dynamically reconfigured by special types of equipment such as routers and switches.

Advantages and Disavantages of Topologies:

1. In Bus Topology, a device communicates with another device on the network sends a broadcast message onto the wire that all other devices , but only the intended recipient actually accepts and processes the message. A failure in network cable or wire will only take down entire LAN.Bus topology is very easy, simple and inexpensive than other topologies.

2. Star Topology is very easy to install but it is expensive due to the cost of central device. Many home networks use the star topology.A failure in any star network cable will only take down one computer’s network access.

3. Tree topology is a combination of star and bus topologies.This network is very easy to extend and facilities the organizations to meet their requirements. In tree topology if central cable breaks then all the nodes goes down.

1. In Ring Topology,All messages travel through a ring in the same direction (either “clockwise” or “counterclockwise”). A failure in any cable or device breaks the loop and can take down the entire network. Ring topologies are found in some office buildings or school campuses.

1. A mesh offers various advantages over other network topologies.Firstly, use of dedicated links guarantees that the each connection can carry its own data load, thus eliminating traffic troubles that can take place when links must be shared by multiple devices.Second is that a mesh topology is robust in nature.

Introduction

· A JSP page is a web page that contains Java code along with the HTML tags.

· When accessed by a client, the Java code within the page is executed on the server side, producing textual data.

· This data, which is surrounded by HTML tags, is sent as a normal HTML page to the client.

· JSP pages typically comprise of:

ü Static HTML/XML components.

ü Special JSP tags

ü Optionally, snippets of code written in the Java programming language called “scriptlets”.

Phase	Description
Page translation	The page is parsed and a Java file containing the corresponding servlet is created.
Page compilation	The Java file is compiled.
Load class	The compiled class is loaded.
Create instance	An instance of the servlet is created.
Call jspInit()	This method is called before any other method to allow initialization.
Call jspService()	This method is called for each request.
Call jspDestroy()	This method is called when the servlet container decides to take the servlet out of service.

Life Cycle Methods

Method	Parent Class
public void jspInit();	javax.servlet.jsp.JspPage
public void _jspService(HttpServletRequest request, HttpServletResponse response) throws javax.servlet.ServletException, java.IO.IOException;	javax.servlet.jsp.HttpJspPage
public void jspDestroy();	javax.servlet.jsp.JspPage

The jspInit(),_jspService(), and jspDestroy() methods of a JSP page are equivalent to the init(), service(), and destroy() methods of a servlet, respectively.

JSP Elements

JSP Tag Type	Description	Tag Syntax
Directive	Specifies translation time instructions to the JSP engine	<%@ Directives %>
Declaration	Declares and defines methods and variables	<%! Java Declarations %>
Scriptlet	Allows the developer to write free-form Java code in a JSP page	<% Some Java code %>
Expression	Used as a shortcut to print values in the output HTML of a JSP page	<%= An Expression %>
Action	Provides request-time instructions to the JSP engine	<jsp:actionName />
Comment	Used for documentation and for commenting out parts of JSP code	<%– Any Text –%>

Directives

— Directives provide general information about the JSP page to the JSP engine.

— page: A page directive informs the engine about the overall properties of a JSP page

<%@ page language=”java” %>

— include: An include directive tells the JSP engine to include the contents of another file in the current page.

<%@ include file=”copyright.html” %>

— taglib: A taglib directive is used for associating a prefix with a tag library.

<%@ taglib prefix=”test” uri=”taglib.tld” %>

— The tag names, their attributes, and their values are all case sensitive.

— The value must be enclosed within a pair of single or double quotes.

— A pair of single quotes is equivalent to a pair of double quotes.

— There must be no space between the equals sign (=) and the value.

Scriplets

— Scriptlets are Java code fragments that are embedded in the JSP page.

<% count++; %>

— The scriptlet is executed each time the page is accessed.

Expressions

— Expressions act as placeholders for Java language expressions.

<%= count %>

— The expression is evaluated each time the page is accessed, and its value is then embedded in the output HTML.

— We can print the value of any object or any primitive data type (int, boolean, char, etc.) to the output stream using an expression.

— We can also print the value of any arithmetic or Boolean expression or a value returned by a method call.

Actions

— Actions are commands given to the JSP engine. They direct the engine to perform certain tasks during the execution of a page.

jsp:include jsp:forward

jsp:useBean jsp:setProperty

jsp:getProperty jsp:plugin

— The first two, jsp:include and jsp:forward, enable a JSP page to reuse other web components.

— The next three, jsp:useBean, jsp:setProperty, and jsp:getProperty, are related to the use of JavaBeans in JSP pages.

— The last action, jsp:plugin, instructs the JSP engine to generate appropriate HTML code for embedding client-side components, such as applets.

Comments

— Comments are useful for documentation purposes.

— The syntax of a JSP comment is

<%– Anything you want to be commented –%>

— We can comment the Java code within scriptlets and declarations by using normal Java-style comments and the HTML portions of a page by using HTML-style comments

<html>

<body>

Welcome!

<%– JSP comment –%>

<% //Java comment %>

<!– HTML comment–>

</body>

</html>

JSP Implicit Objects

The JSP container makes available implicit objects that can be used within scriptlets and expressions, without the page author first having to create them

Identifier	Class or Interface	Description
application	interface javax.servlet.ServletContext	Refers to the web application’s Environment
session	interface javax.servlet.http.HttpSession	Refers to the user’s session
request	interface javax.servlet.http.HttpServletRequest	Refers to the current request to the page
response	interface javax.servlet.http.HttpServletResponse	Used for sending a response to the client
out	class javax.servlet.jsp.JspWriter	Refers to the output stream for the page
page	class java.lang.Object	Refers to the page’s servlet instance
pageContext	class javax.servlet.jsp.PageContext	Refers to the page’s environment
config	interface javax.servlet.ServletConfig	Refers to the servlet’s configuration
exception	class java.lang.Throwable	Used for error handling