An Introduction to JDBC
At Mitre, we collect information from the Internet using commercial search engines such as Altavista and Lycos for a variety of topics. This information is stored as a collection of text documents for any topic and can be searched via keywords. We use the public-domain search engine Glimpse from the University of Arizona to index and search the document collection.
Some of the document collections can be fairly large (over 1500 documents). If a common keyword is entered, the list of matching documents will be large. We display the results from the search engine using Java and JDBC to avoid scanning long lists of matching documents. Java was used to build a 3-D space and plot circles at locations representing the frequency of the occurrences of keywords in a document. JDBC was used to retrieve the titles of the documents stored in a table. Passing all the titles of all documents in the collection as parameters to the Java applet would significantly increase the time to load the applet.
Glimpse returns the frequency of occurrence of a keyword in a document. We use that number to locate a circle representing the document in 3-D space (see Figure 3). Each axis represents a keyword. If fewer than three keywords are entered, documents will be displayed in a plane or on a line. If more than three keywords are entered, three or fewer keywords must be chosen in order to display matching documents.
The frequency of occurrence of keywords is normalized for each axis, and the frequencies of keywords in documents are passed as parameters to the applet. The color of the circle was computed based on the position of the circle in the three axes. Red is used for documents on the z-axis, green for documents on the y-axis and blue for documents on the x-axis. Brighter shades of the three primary colors are used for documents with higher keyword frequencies. A mix of the primary colors is used for circles which contain more than one keyword.
JDBC is used to retrieve the titles for documents containing non-zero occurrences of the keywords. This number is usually fewer than the total number of documents when a fairly unique keyword is used. When the mouse is located over the document, a window is displayed with the document's title. Sometimes, more than one document can have the same frequency of occurrence of a keyword. In such cases, the window displays multiple titles of documents. The color of the circle changes to white to indicate the document where the mouse is located. An option to click on a box in the window is provided and will retrieve the text corresponding to the document in a separate window.
This article has described the basics of working with JDBC under Linux: the design of JDBC, the installation of JDBC for MySQL and example code to retrieve/store data. Metadata statements can be used to interrogate the structure of a database and its tables. Finally, we looked at an example using a search engine with JDBC and Java. Viewing the results from a Java applet made the user's task more interesting than it would have been through a CGI program.
The listing referred to in this article is available by anonymous download in the file ftp.linuxjournal.com/pub/lj/listings/issue55/2846.tgz.
Manu Konchady (firstname.lastname@example.org) works at Mitre Corporation developing software for information retrieval. As the lone user of Linux in a group of 50, he is striving to promote its many benefits.
Practical Task Scheduling Deployment
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
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This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide