hpr-knowledge-base/hpr_transcripts/hpr0913.txt

Episode: 913
Title: HPR0913: Exchanging Data Podcast 1
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr0913/hpr0913.mp3
Transcribed: 2025-10-08 04:48:46

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My name is Dan Fry and over the next few podcasts I'm going to explain how to share data
between your website and any number of external applications.
The concepts and ideas used in these podcasts is based on my work to complete the open schedule
web application and companion Android application.
The open schedule is a web application that allows conference organizers to administer
and publish their conference schedules.
The data is publicly available over the internet and is able to be accessed by the Android
application anytime the conference goes which to reference the schedule.
These podcasts will address the following.
In this podcast I will identify and explain the formats used for exchanging data over
the web.
The next podcast will explain how to build restful web services that can be used for accessing
the data stored on the server.
The third podcast will show how the data can be consumed by the clients.
Lastly, I will talk about possible ways to make these solutions scale.
To help explain these concepts I'm going to build a simple web application about a fictional
restaurant that wants to make their menu available online as well as on an Android application.
The same web service API can also be used by a restaurant review website that wants to
display the restaurant's menus along with their reviews.
All of the data and applications mentioned in these podcasts will be available on GitHub.
Please stay tuned to the end of the podcast for information on accessing these resources.
I'm going to start by talking about the data formats used to transfer data over the internet.
There are numerous data exchange formats.
For the purposes of this podcast I will focus on the few that are lightweight and easily
parsable by the client languages.
I would also like to mention that this will be a simplistic view of these data formats.
The first format is the extensible markup language or more commonly known as XML.
It is a lightweight textual data representation that was designed for simplicity and ease
of use across the internet.
It is easily human as well as machine readable.
XML allows developers to create context-specific data structures that are relevant to their
own applications.
Opening is very straightforward.
Opening tags are enclosed inside less than greater than symbols.
Closing tags are enclosed in a less than and a forward slash together and a greater than
tag.
The opening closing tag names must match to be well formed and this includes their let
a case as well.
There usually is one route opening and closing tag.
Tags can also be nested inside of parent tags.
XML supports validation by the much older document type declarations or DTDs and XML schemas
which is the current standard.
However, these validation methods are out of scope for this podcast.
If you are interested in further information regarding XML, please check out the XML page
in Wikipedia or other sources around the internet.
For an example, XML document for our restaurant application, please see the sample data section
on the GitHub repository.
The next data format is called JavaScript Object Notation or simply referred to as JSON.
Wikipedia defines JSON as a lightweight text-based, open-standard design for human readable data
interchange.
It is derived from the JavaScript scripting language for representing simple data structures
and associative arrays called objects.
Despite its relationship to JavaScript, it is language independent with parses available
for most languages.
Attributes and JavaScript are denoted by opening and closing curly braces.
Key value pairs make up the attributes inside JavaScript objects and are separated by
commas.
For well-forbidess, keys as well as text and date values should be enclosed in double quotes.
Number values should not be in double quotes.
Attribute values need not be simple types like strings or numbers.
They can contain arrays of objects as well, which can be simple values or complex objects.
Arrays and JavaScript are denoted with opening closing square braces and follow the same
rules mentioned earlier.
JSON does allow the attribute value to be a JavaScript function, but that is out of
scope for this podcast.
For an example, JSON document for our restaurant application, please see the sample data section
of the GitHub repository.
The last data type I will talk about is called JSON With Padding or simply JSON P for short.
JSON requests cannot access data that originates on a different server than the calling application.
When making a JSON P request, the request must contain a callback function that instructs
the response on how it should be processed when the calling application receives it.
The callback function is the padding in JSON P. To explain why this is important, imagine
you are writing a website and you want to include a Google search result list in your
page.
In this situation, you would make a JSON P request to Google's Ajax API.
The callback function you provide would instruct your application to draw the area on the
page where the Google search results should be rendered.
JSON P requests are somewhat out of scope for this podcast, but I wanted to make you aware
of them as you may want to share your web services with more than just your own website or
mobile applications.
JSON P requests allow other website developers to integrate with your public data.
Let's close out this podcast by taking a look at the data model we'll be using in our
sample application.
The restaurant can have any number of menus such as a breakfast menu, lunch menu, dinner
menu, dessert menu, etc.
Each menu can have sections like appetizers or eggs and omelets on a breakfast menu, salads,
that type of thing.
Each section can have any number of menu items and each item will require a name, description,
and a price.
The data model is very simple for this application.
In the next podcast, I'll be looking at building restful web services that publish the data
model up onto the internet, making it available for consumption by client applications.
Just to reiterate, client applications could mean your website, another website, or mobile
application.
It could be any or all of those types of applications.
Thank you for listening.
My name is Dan Frey and I'm the senior web architect I had no one corporate.
I co-host the MythTVcast podcast and I'm a regular co-host on the Linux link tech show.
The MythTVcast podcast can be found at MythTVcast.com.
The Linux link tech show can be found at TLLTS.org and streams live every Wednesday night at 8.30
PM Eastern Standard Time.
I can be reached on Google Plus, at Plus Daniel Fry, on Twitter, and Identica at DM Fry and
on Facebook, at Facebook.com slash DM Fry.
The projects in this presentation can be found on GitHub under github.com slash DM Fry slash
exchanging data presentation.
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