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Title:
Fundamentals of XML - Data Wranging with MongoDB
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Description:
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In case you're not terribly familiar with XML, let's spend
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a few minutes talking syntax. Even if you are familiar,
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it might make sense to follow along with this little
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review. So in XML, elements are the basic building blocks
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of an XML document. Now an XML element is composed
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of an open tag and a closed tag, now this
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is some data drawn from the New York Times developer
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API Encourage you to have a look at this site.
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We are going to look at some data from the most
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popular API. These are for example articles that are most frequently
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emailed among readers of the New York Times. Okay, so
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let's look at a couple of examples here. So, the first
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thing that we might notice about this particular document is
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that we have some tags for num results or some elements
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that have to do with the number of results. So,
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this is actually result set from having done a query to
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the most popular API and we've got a, an
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element that tells us how many results were identified
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by our query. And then the list of results
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follows. Now this happens to be a single result here.
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And we can see that this result begins right
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here with this open tag and closes right here
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with this close tag. Okay. Now just as a
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couple of other examples of the data within this particular
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result, we can take a look at the byline, note that
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it's got a close tag, as well. And some of the
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other elements, here if you note the title for example, this
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happens to be an article about bedbugs. Okay. So, this provides an
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example using some really nicely named tags. We know what these
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mean. Now, there's another aspect of XML that we need to concern
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ourselves with especially given some of the exercises that we're going
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to have. Later on. And those have to do with attributes for
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XML elements. Now, this document provides a number of very
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nice examples of elements in XML. But what we don't
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have here are any examples of attributes for any of
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these elements being used. So what I'd like to do here
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is talk about essentially the two types of data that
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we're going to look at that have been encoded in XML. One
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is this more documented oriented type of XML, which is
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originally the type of data that XML was designed to encode.
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But then we can also take a look at
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something like this. Okay, now this is actual data from
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the OpenStreetMap project. This is a pretty close
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zoomed in view from OpenStreetMap of West Belmont
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avenue. Particularly the 1000 block. And you can see right
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here, there's a Giardano's Restaurant here. Giardano's is a famous
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pizza chain in Chicago. So, this is data that is
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essentially from a layer on top of that particular map.
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This is data that is human created. So, users
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of OpenStreetMap have actually added this data on
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top of the map data. And what I want to point out here is that this is very much
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not document oriented. This is just data. Okay? And
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a lot of times you see HTML used in this
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way, you'll see that attributes are heavily used. So
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in this particular example, this is the node that represents
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the Giordano's restaurant. We can see that there is
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a number of attributes specified for this particular element.
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Common among them are the latitude and longitude attributes
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that this particular annotation applies to. So, essentially what
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this data element provides is a mapping from geographic
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coordinates to more common street address coordinates. Okay? So
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this is a good example of attributes in XML
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and there's one other thing that I want to point
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out here. And that is this type of tag here.
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Now in this particular data they're doing something that I probably
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wouldn't do, but it is the type of thing that
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you're going to see as a data scientist and likely already
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have. Essentially, they've just got a bunch of key value
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pairs that are encoded in something called a tag element. And,
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in this case, none of these tag elements have a
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close tag. Instead, they use this special xml syntax where you
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can simply create what are called empty tags, that
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is tags that don't have any content. All of
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the data for this type of tag is contained
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directly within its attributes. So the most emailed example
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here provides us a nice example of document oriented
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XML with lots of content inside the elements. And
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this particular example from your OpenStreetMap project provides us
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with other end of this spectrum which is very
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data oriented XML where all or almost all of the data
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is contained within attributes for the individual elements and in this
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types of cases, you often have mostly or at least many
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empty elements within the XML data that you are looking at.
