library(knitr)
## Warning: package 'knitr' was built under R version 3.3.3
library(XML)
## Warning: package 'XML' was built under R version 3.3.3
library(jsonlite)
## Warning: package 'jsonlite' was built under R version 3.3.3
library(RCurl)
## Warning: package 'RCurl' was built under R version 3.3.3
## Loading required package: bitops

HTML

doc1 <- "https://cdn.rawgit.com/mdacampora/DATA607-Data-Acquisition-and-Managment/5b06e314/books.html"

books1 <- readHTMLTable(getURL(doc1))

kable(books1)
Title Author Pages Topic Year
Tools of Titans Tim Ferriss 900 Health, Wealth, and Widsom 2017
The Second Law P.W. Atkins 230 Physics 1984
Zero to One: Notes on Startups, or How to Build the Future Peter Theil, Blake Masters 224 Business 2014

XML

doc2 <- "https://cdn.rawgit.com/mdacampora/DATA607-Data-Acquisition-and-Managment/5b06e314/books.xml"

books2 <- xmlToDataFrame(getURL(doc2))

kable(books2)
Title Author Pages Topic Year
Tools of Titans Tim Ferriss 900 Health, Wealth, and Widsom 2017
The Second Law P.W. Atkins 230 Physics 1984
Zero to One: Notes on Startups, or How to Build the Future Peter Theil, Blake Masters 224 Business 2014
### JSON 
doc3 <- "https://cdn.rawgit.com/mdacampora/DATA607-Data-Acquisition-and-Managment/5b06e314/books.json"

books3 = fromJSON(doc3)

kable(books3)
Title Author Pages Topic Year
Tools of Titans Tim Ferriss 900 Health, Wealth, and Widsom 2017
The Second Law P.W. Atkins 230 Physics 1984
Zero to One: Notes on Startups, or How to Build the Future Peter Theil, Blake Masters 224 Business 2014

While the dataframes look identical, it appears the data structure for JSON is more like a dictionary and the data may be stored differently.