The four parts of a This presentation is on URLs. URL sounds URL exotic – it stands for universal resource locator URLs – uniform resource locators – but it is just a geek term for a Web address. A IT skills: compose URLs URL is the address of a resource on the Web. IT concepts: parts of a URL, shortened URLs, domain names, directories, file names You’ve typed URLs into Web browsers many times, but may not have thought about the meanings of each of the four parts of a URL. We will review them and also mention This work is licensed under a Creative Commons Attribution-Noncommercial- Share Alike 3.0 License. shortened URLs. In order to understand the parts of a URL, we will also cover domain names, directories and file names. Communication URLs are a technical topic, but understanding Where does this topic fit? them will also help you use the Web, so we technology • Internet concepts include this presentation at two places in our – Applications class outline. – Implications – Technology • Internet skills – Application development – Content creation – User skills URL – a Web To retrieve a page from a Web site, you type its URL, uniform resource locator address URL into the box at the top of the browser and hit enter. The browser then retrieves the page http://som.csudh.edu/fac/lpress/shortbio.htm from the server and displays it. URL is just a fancy way to say the Web address of the page. request In this example, a short professional biography page Client Server that is stored at the listed URL is retrieved and displayed. The four parts of a If you look at URLs, you see that they can be URl Four parts of the URL broken down into four parts. Note that some of the parts may be omitted at times – we’ll talk about that later. For now, let’s take a look at http://som.csudh.edu/fac/lpress/shortbio.htm each of the four parts. http://som.csudh.edu/fac/lpress/shortbio.htm http://som.csudh.edu/fac/lpress/shortbio.htm http://som.csudh.edu/fac/lpress/shortbio.htm Part 1 – this is a The URL prefix “http://” indicates that this is Web page http:// the locator for a Web document that should be retrieved and displayed. It turns out that Web browsers can also function as clients for other http://som.csudh.edu/fac/lpress/shortbio.htm services like file transfer, but that is seldom done. For that reason, one can often omit the “http://” since most browsers will plug it in for you. Part 2 – the domain The next part of our example URL reads name of the server The domain name “som.csudh.edu”. That is the domain name of the server. Domain name is another fancy geek word – it is the name of the computer the server program is running on. We will say more about http://som.csudh.edu/fac/lpress/shortbio.htm domain names in another presentation. For now, it’s enough to say that the domain name identifies a unique computer on the Internet. Part 3 – the The next part of the URL is the directory or The directory directory the page is folder containing the page we are looking for. in on the server http://som.csudh.edu/fac/lpress/shortbio.htm Every computer has many files in storage. We would quickly become confused in trying to root locate a single file in a list of say 100,000 names. For that reason, we organize our storage staff fac admin into hierarchical directories, sub-directories, sub-sub-directories and so forth. * lpress jsmith ... jdoe Here we have three sub-directories – for staff, faculty and administrators. Since I am a faculty member, my directory, named “lpress,” is a subdirectory of the fac directory. Each faculty member – jsmith, jdoe, and the rest would have directories in the fac directory. Part 4 – the name of The final part of the URL is the name of the file The file name the file on the server we wish to retrieve, in this case “shortbio.htm.” http://som.csudh.edu/fac/lpress/shortbio.htm Since shortbio.htm is in the lpress directory, the Web server will send that file back to the client, root which will display it. The user can then read my short biography. staff fac admin Note that the file name has two parts separated ... lpress jsmith jdoe by a dot. The suffix or “extension” indicates what type of file it is. The suffix “htm” means shortbio.htm that this is an HTML file, in other words a Web page. (We will say more about HTML later). Shortened URLs Let’s look at a couple more things concerning URLs may be shortened URLs. http://www.csudh.edu/studentaffairs/financialaid/faq. shtml#apply_for_scholarships For a start, you can save space by shortening a URL. If you try them out, you will see that both http://bit.ly/djeREW of the links shown here are to the same page. There are many URL shortening services on the Internet. I used one called bit.ly to create this (I shortened the URL using the service at http://bit.ly. There example. are others that do the same thing.) Shortened URLs can Be cautious when clicking on shortened URLs. be risky. Know the source of a shortened URL Shortened URLs hide the actual domain name, so you cannot tell where they link to by looking at them. http://bit.ly/9dLHk5 Click the link shown here to see why you should only go to shortened URLs from trusted sources. Most Web clients As mentioned previously, if you delete the assume http:// by You can delete the http:// http://, the client will assume the message is for default a Web server and request the page as if the http:// had been included. som.csudh.edu/fac/lpress/shortbio.htm Default file names If you delete the file name, the Web server will You can delete the file name look for a file with a default name, which is specified by the server administrator. http://bpastudio.csudh.edu/fac/lpress/ Traditional default names are index.htm, Index.html, default.htm, and default.html. The Web server will look for a file with a default name, which is specified by the server administrator. Traditional default names are index.htm, Index.html, default.htm, and default.html. Summary Here we summarize the meaning of the four URL summary parts of a URL. In addition to learning about the parts of a URL, we saw that they may be http://som.csudh.edu/fac/lpress/shortbio.htm shortened using a service like Bit.ly and that This request is for a Web (http) server some parts of the URL were optional. The server program is running on a computer with the domain name som.csudh.edu Look in a subdirectory called fac/lpress If there is a file called shortbio.htm, send it back to the client to We also learned about domain names, be displayed; if not, send an error message back to the client directories and file names. Domain name = the unique name of a computer on the Internet Self-study questions 1. Without looking back, can you describe the four parts of a URL and explain what each means? 2. What happens if you misspell the file name in a URL? 3. What happens if you misspell the domain name in a URL? 4. Can you omit the domain name? 5. What happens if a URL shortening service like bit.ly goes out of business?
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