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This video introduces JSON.
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Let's start by talking about its pronunciation.
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Some people call it Jason, and some call it J-sahn.
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I'll do a little bit of
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investigation and discovered that the
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original developer of JSON calls
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it JSON so, I'll do that too.
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Like XML, JSON can be thought of as a data model.
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An alternative to the relational data
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model that is more
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appropriate for semi-structured data.
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In this video I'll introduce the
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basics of JSON and I'll
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actually compare JSON to the
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relational data model and I'll compare it to XML.
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But it's not crucial to have
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watched those videos to get something out of this one.
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Now among the three models
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- the relational model, XML, and
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JSON - JSON is by
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a large margin the newest,
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and it does show there aren't
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as many tools for JSON
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as we have for XML and
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certainly not as we have for relational.
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JSON stands for Javascript object notation.
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Although it's evolved to become pretty
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much independent of Javascript at this point.
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The little snippet of JSON in the corner right now mostly for decoration.
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We'll talk about the details in just a minute.
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Now JSON was designed
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originally for what's called
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serializing data objects.
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That is taking the objects that
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are in a program and sort
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of writing them down in a
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serial fashion, typically in files.
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one thing about JSON
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is that it is human readable,
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similar to the way xml
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is human readable and is
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often use for data interchange.
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So, for writing out, say
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the objects program so that
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they can be exchanged with another
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program and read into that one.
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Also, just more generally, because
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JSON is not as rigid
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as the relational model, it's generally
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useful for representing and for
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storing data that doesn't
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have rigid structure that we've been calling semi-structured data.
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As I mentioned JSON is
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no longer closely tied to
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Many different programming languages do
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have parsers for reading JSON
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data into the program and
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for writing out JSON data as well.
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Now, let's talk about the basic
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constructs in JSON, and as
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we will see this constructs are recursively defined.
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We'll use the example JSON
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data shown on the screen
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and that data is also available
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in a file for download from the website.
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The basic atomic values in JSON are fairly typical.
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We have numbers, we have strings.
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We also have Boolean Values
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although there are none of those
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in this example, that's true and false, and no values.
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There are two types of composite
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values in JSON: objects and arrays.
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Objects are enclosed in curly
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braces and they consist
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of sets of label-value pairs.
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For example, we have an
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object here that has a first name and a last name.
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We have a more -
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bigger, let's say, object here
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that has ISBN, price, edition, and so on.
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When we do our JSON demo,
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we'll go into these constructs in more detail.
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At this point, we're just introducing them.
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the second type of composite
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value in JSON is arrays,
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and arrays are enclosed in square
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brackets with commas between the array elements.
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Actually we have commas in the objects
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as and arrays are list of values.
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For example, we can see
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here that authors is a
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list of author objects.
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Now I mentioned that the constructs
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are recursive, specifically the values
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inside arrays can be anything,
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they can be other arrays or objects,
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space values and the values
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are making up the label value
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pairs and objects can also
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be any composite value or a base value.
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And I did want to
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mention, by the way, that sometime
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this word label here for
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label value pairs is called a "property".
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So, just like XML, JSON
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has some basic structural requirements in
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its format but it doesn't
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have a lot of requirements in terms of uniformity.
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We have a couple of examples
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of heterogeneity in here, for
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example, this book has an
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edition and the other one
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doesn't this book has a remark and the other one doesn't.
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But we'll see many more examples
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of heterogeneity when we do
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the demo and look into JSON data in more detail.
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Now let's compare JSON and the relational model.
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We will see that many of
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the comparisons are fairly similar
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to when we compared XML to the relational model.
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Let's start with the basic structures underling the data model.
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So, the relational model is based on tables.
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We set up structure of
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table, a set of columns, and
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then the data becomes rows in those tables.
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JSON is based instead on
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sets, the sets of label
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pairs and arrays and as we saw, they can be nested.
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One of the big differences between
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the two models, of course, is the scheme.
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So the Relational model has a
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Schema fixed in advance,
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you set it up before you
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have any data loaded and then
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all data needs to confirm to that Schema.
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JSON on the other other
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hand typically does not require a schema in advance.
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In fact, the schema and the
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data are kinda mix together
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just like an xml, and
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this is often referred to as
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self-describing data, where the
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schema elements are within the data itself.
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And this is of course typically
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more flexible than the to a model.
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But there are advantages to having schema [sp?]
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as well, definitely.
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As far as queries go, one
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of the nice features of the
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relational model is that there
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are simple, expressive languages for clearing the database.
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In terms of JSON, although a
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few New things have been proposed;
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at this point there's nothing widely
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used for querying JSON data.
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Typically JSON data is
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read into a program and it's manipulated programatically.
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Now let me interject that this
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video is being made in February 2012.
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So it is possible
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that some JSON query languages
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will emerge and become
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widely used there is just
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nothing used at this point.
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There are some proposals.
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There's a JSON path language,
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JSON Query, a language called jaql.
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It may be that just like
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XML, the query language are
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gonna follow the prevalent use
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of the data format or the data model.
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But that does not happened yet, as of February 2012.
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How about ordering?
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One aspect of the relational model is that it's an unordered model.
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It's based on sets and
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if we want to see relational
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data in sorted order then we put that inside a query.
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In JSON, we have arrays as
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one of the basic data structures, and arrays are ordered.
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Of course, there's also the fact like
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XML that JSON data is
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often is usually written files
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and files themselves are naturally ordered,
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but the ordering of the data
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in files usually isn't relevant,
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sometimes it is, but
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typically not finally in
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terms of implementation, for the
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relational model, there are
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systems that implement the relational model natively.
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They're very generally quite
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efficient and powerful systems.
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For JSON, we haven't yet
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seen stand alone database systems
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that use JSON their data
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model instead JSON is
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more typically coupled with programming languages.
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One thing I should add however
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JSON is used in NoSQL systems.
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We do have videos about NoSQL
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systems you may or may not have, have watched those yet.
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There's a couple of different ways that JSON is used used in those systems.
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One of them is just as
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a format for reading data
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into the systems and writing data out from the systems.
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The other way that it is
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used is that some of the
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note systems are what are
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called "Document Management Systems" where
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the documents themselves may contain
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JSON data and then the systems
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will have special features for manipulating
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the JSON in the document is better stored by the system.