Note: A path is a series of vertices and edges. For the graph to the left that's a series of blue circles (vertices) and black lines (edges).
A graph is a set of vertices and edges. A vertex is a point of in the graph and it's connected to other vertices by edges. A vertex is also referred to as a node. A graph is basically just a means of representing something. The reason it's being brought up now: the internet is easily represented as a big graph.
There's one other computer "thing" that you may have unknowingly worked with as a graph: your computer's file system.
This is a more simplistic graph structure known as a tree. Your computers file structure forms a tree - in most cases - and does so because each file is contained within only one folder. In the example above, purple nodes represent folders and blue nodes represent files. We can see that each file or folder is connected to exactly one folder directly above it in the hierarchy. We refer to this directly above node as the parent node while the node below is the child node. In the example above, one relationship is between the "cps1" node and the "test.html" node. Here the cps1 node isthe parent and the test.html node is the child.
When trying to reference pictures and other files locally in our HTML code we had to locate the files we needed by a file path. That path simply stated how to get from one file, go through the hierarchy of folders, and finally reach another file. In the example above, to get from index.html to the file page2.html we would take the path: index.html -> public_html -> cps1 -> page2.html. Since there is at most a single edge between any two nodes in my tree above, I only have to state the order of vertices to visit on the path and its The important property that distinguishes trees as a special type of graph is that trees do not have cycles. A cycle is a path of vertices and edges that forms a connected loop. A path is simply an ordered set of vertices such
Graphs - example graph: how do you find the shortest path from node A to all other nodes - how do we represent a graph (in a computer or in general) - tree vs. general graph - what is a cycle - what is the degree of a node - search through a graph (DFS, BFS) - directed vs undirected graphs - traversing all edges in a graph: mailman's walk - deciding if two trees (or two graphs) are the same (isomorphic)?
The internet is a worldwide connected network of computers. There are several local networks (such as the Duke University network) and many individual computers (possibly your PC at home?) that are connected to make the internet. One of the most notable uses of the internet is the world wide web, which could be the web or www for short. The web is made up of set of hypertext documents (HTML documents) that are publicly shared with the world, which we know as webpages. (Note that HTML stands for HyperText Markup Language.) The web is not the internet. The web is just one of the most popular uses of the internet. Another extremely popular use of the internet is email.
The internet began life somewhere in the mid 1960's. It's a little bit hard to define exactly what was the starting point. In 1962 J. C. R. Licklider of MIT proposed the "glactic network" idea of many different computers connected together and sharing information. From 1962 until 1967 he and other researchers start solving the theoretical problems that had to be overcome before this "galactic network" could be created.
A project started being funded by the Department of Defense's small research office ARPA (Advanced Research Project Agency) somewhere around 1966. Finally, in 1969, the first computer-to-computer message was sent. A network of computers began to be formed and came to be referred to as the ARPANET. In 1972 the first formal demonstration of the ARPANET was made to the scientific community and email was invented. Around this time other communities also started developing their own networks. While this was a great development, it brought about the problem of having separate networks that couldn't necessarily communicate with each other. To have a more unified, single network researchers for ARPA came up with the idea of a "network of networks". Each local area network (LAN) could communicate within its area however it liked. Yet, when communicating with other networks, each would have to use a single established protocol.
Internet vs Web
- the internet is the interconnection of computer systems worldwide
- the 'web' is the set of hypertext documents (HTML webpages) that
you can view over the internet using a web browser
- another major internet application is, of course, email
- LAN vs WAN networks
- url address: protocol://Internet address/page
- global DNS (domain name server) information
- first graphical web browser began in 1993
- http stands for hypertext transfer protocols
- telnet is a software package for remotely logging onto other comptuers
(mention the options on the course resources page)
- ftp: file transfer protocol
- internet began in the mid 1960's
- 1962 J. C. R. Licklider of MIT proposes "the galactic network" idea
- 1962 - 1967 he and other researchers build the theoretical foundation
for this network
- project started being funded by Dept. of Defense's small research
office ARPA (Adv. Research Proj. Agency) ~1966?
- 1969: first computer-to-computer message was sent
- 1972: first formal demonstration of the ARPANET to the
scientific community and email is invented
- other communities started developing similar networks
- researchers at ARPA came up with the idea for a "network of networks"
- DNS system is devised by Robert Kahn and Vinton Cerf
- DNS has the form: MyName@MyComp.Dept.School.edu
- these symbolic addresses actually stand in place of
IP numbers, which are a bit hard to remember
- TCP/IP transmission control protocol/internet protocol
- NSF started the NSFNet in 1984 to bring Internet technology
to all academic and professional communities
- 1995: US Gov. formally accepts the term Internet for the name of
this network of networks
- 1995: NSFNet shuts down and we're left with Internet Service Providers (ISP's)
Internet Access
- signals get passed along between computers (analog vs. digital)
- when internet access was done with just regular dial-up lines
(and shared with phones) then analog was used
- a modem was the device that converted between the binary signals of
0's and 1's in a computer to the analog signal for telephone lines
- now more common are dedicated lines used just for internet access
- fiberoptic cable choices are the next step to take
- need to give some idea of bits, bytes, and file sizes
- note what is happening when your webpage is viewed by a web browser