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What Is Data Munging?

Data munging means taking data that's stored in one format and changing it into another format. The term "data munging" has an ironically mixed etymological origin. The following definition is taken from version 4.3.0 of the Jargon file:[1]

[1] See http://www.tuxedo.org/~esr/jargon/html/entry/munge.html.Used with permission. Available in print, as The New Hacker's Dictionary, edited by Eric S. Raymond, 3rd ed. (MIT Press, 1996), http://www-mitpress.mit.edu.

munge /muhnj/ vt.

1. [derogatory] To imperfectly transform information. 2. A comprehensive rewrite of a routine, data structure or the whole program. 3. To modify data in some way the speaker doesn't need to go into right now or cannot describe succinctly (compare mumble). 4. To add spamblock to an email address.

This term is often confused with mung, which probably was derived from it. However, it also appears the word `munge' was in common use in Scotland in the 1940s, and in Yorkshire in the 1950s, as a verb, meaning to munch up into a masticated mess, and as a noun, meaning the result of munging something up (the parallel with the kluge/kludge pair is amusing). The OED[2] reports `munge' as an archaic verb meaning "to wipe (a person's nose)".

[2] Oxford English Dictionary: http://www.oed.com

Perl, with its excellent text-processing capabilities and high performance, is ideally suited to the task of data munging. In this chapter we'll focus on those munging capabilities most relevant to processing Oracle data. If you want to learn more, we recommend the book, Data Munging With Perl, by David Cross (Manning, 2001), which we've found to be invaluable in our own data-munging efforts:

How Data Munging Works

Figure D-1 illustrates graphically how data munging works. As shown in the figure, there are several distinct components and steps involved in a data-munging operation:

Figure D-1. Basic data-munging principles
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The data source

On one side of the munging equation is our data source, or initial wellspring of data. This can be anything from a raw binary file to a stream of digital output from a remote MySQL database. Because Perl was designed from the start to be one of the fastest text-processing languages available, it is able to process and transform data at a very high speed. For this reason, Perl is an ideal language for data munging.

The munge operation

Once the source data is extracted, we begin our munge operation. This operation can be any kind of transformation. We can reverse data, expand data, and recombine data. We can munge it through regular expressions or sprintf style commands, as in Appendix C, or we can parse it through complex data trees. Although Perl abounds with such techniques, there are three controlling paradigms:

Sort algorithms

Some of the world's brightest mathematicians have created sort algorithms, and all of these algorithms can be programmed in Perl. The language is also packed with built-in commands, such as sort and map, and Perl-specific sort techniques, such as the Schwartzian transform.[3]

[3] http://www.perlfaq.com/cgi-bin/view?view_by_category=sorting

Data structure and design

The central munge operation must be able to represent the data structures for both the source and the sink (which is essentially the destination), no matter how complex. It must also be able to transform data from one structure into the other. Because Perl's referenced structures are virtually unbounded in extent, Perl is a perfect language for handling such transformations.

Business rules

We can easily encapsulate business rules within Perl modules, and can thus provide reusable, business-specific data transformations.

The data sink

Our transformed data is finally deposited within a chosen data sink. A data sink works conceptually the same way as a "heat sink" does in engineering; it sucks away the final output from a processing operation. In data munging, this output is the final data generated, rather than the unwanted "heat" in the process. (In engineering, the heat would be generated by a piece of electrical equipment such as a satellite or a laptop computer.)[4]

[4] Another analogy is that of sinking a putt in golf. Getting the data in the right hole is the final process destination in our data-munging operation.

The Art of Algorithms

There are legions of algorithms used with data munging. The most venerable source for all of them is Donald Knuth's The Art of Computer Programming, volumes 1-3 (Addison-Wesley, 1998). Professor Knuth began writing this magnum opus in 1962, and it is divided into several volumes as follows:

Volume 1: Fundamental Algorithms
Volume 2: Seminumerical Algorithms
Volume 3: Sorting and Searching

We make use of his Soundex algorithm, from volume 3, later in this appendix, and you can check out Professor Knuth's own home page here:

http://www-cs-faculty.stanford.edu/~knuth

Those who already have volumes 1 through 3 will be happy to know that Professor Knuth is also aiming to complete the following volumes:

Volume 4: Combinatorial Algorithms
Volume 5: Syntactic Algorithms

For a more Perl-based approach, check out the following excellent book, written by several of the main authors behind perldoc:

Mastering Algorithms with Perl, by Jon Orwant, John Macdonald, and Jarkko Hietaniemi (O'Reilly & Associates, 1999)[5]

Enter the Real World

You may have spotted a problem with Figure D-1. Yes, it's just too spotless and clean for the real world. One data source, one munge operation, and one data sink. How convenient. If you've ever carried out telecom call transfers, share deal transfers, or any other major corporate data transfer, you'll know that data-munging operations often tend to look a bit more like Figure D-2.

Figure D-2. A real-world data-munging operation
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But this is no problem for Perl. Although Figure D-2 is complex, that's just fine, because Perl is also designed to be complex. That allows it to map itself to the real world's necessary complexity. Or, in the words of Mr. Wall himself:[6]

[6] Second State of the Onion address, from the 1998 Perl Conference, http://www.perl.com/pub/a/1998/08/show/onion.html

You have a deep desire to turn the complex into the simple, and Perl is just another tool to help you do that just as I am using English right now to try to simplify reality. I can use English for that because English is a mess.

This is important, and a little hard to understand. English is useful because it's a mess. Since English is a mess, it maps well onto the problem space, which is also a mess, which we call reality. Similarly, Perl was designed to be a mess (though in the nicest of possible ways).

This is counterintuitive, so let me explain. If you've been educated as any kind of an engineer, it has been pounded into your skull that great engineering is simple engineering. We are taught to admire suspension bridges more than railroad trestles. We are taught to value simplicity and beauty. That's nice. I like circles too.

However, complexity is not always the enemy. What's important is not simplicity or complexity, but how you bridge the two.

In the next section, we'll take a look at a real-world Oracle data transfer and illustrate how Perl can help munge the data. We'll later point you towards the many Perl modules that you can use to invoke the specific conversion or formatting operations you need in order to transform your data appropriately.

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