I would add:

You'll want to learn first how to import the XML data which should be pretty easy. Then how to save it as relational data - meaning that it's the data is extracted and stored in MySQL tables. Here's an example of what I'm talking about using the XML from the link you posted and updating it every couple minutes.

DataCollectionDate Smode rTemp cTemp comp evapfan

----------------------- ------------ -------- ------- ---------- ----------

2016-04-23 16:09:48.023 Refrigerate -4.3 F -8.1 F Relay On Relay On

2016-04-23 16:11:48.023 Refrigerate -2.3 F -8.3 F Relay Off Relay On

2016-04-23 16:13:48.023 Refrigerate -5.8 F -2.1 F Relay On Relay Off

2016-04-23 16:15:48.023 Refrigerate -1.3 F -8.1 F Relay On Relay Off

2016-04-23 16:17:48.023 Refrigerate 4.9 F -7.4 F Relay Off Relay Off

2016-04-23 16:19:48.023 Refrigerate 0.3 F -8.6 F Relay On Relay On

I noticed that there's widgets out there that allow you to use mySQL data to create a graph, one example is below. For shredding XML the key is to understand XPath - it's not hard at all. Here's some good sites to get you started:

querying XML in MYSQL

MYSQL Tutorial[/url]

XML basics

XPath Basics (key for working with XML)

GoDaddy Graph Widget