This is the act of extracting data from websites either manually or automatically. The different methods have different pros and cons. Extracting data manually allows for one to gather specific data from a website; however, the extraction is slow and arduous. Extracting data automatically is time efficient; however, the data gathered is not as specific as manual scraping.
This means a user will manually visit a website, navigate to a specific file, download the file to a specific location and name the file. This process is very time consuming, however still has benefits. It requires little to no coding ability and is unlikely to violate any fair use laws in the contexts of downloading from publicly stored books. If only certain books are required, manual scraping allows for human filtering which in cases where the boundaries cannot be easily defined/written in code can be faster than automatic scraping. For a small set of data, this may be the optimal method considering the amount of people working on a project. However, for a larger set of data other methods should be used.
Automatic scraping involves writing a code/script to download a series of files. Once written
this method is much faster than manual scraping however has some significant drawbacks. While web scraping is not officially against American Law, some may see it as against the fair use policy to disobey the guidelines set out in the
robot.txt file. The
robot.txt file is a file that shows what types of robots are allowed to visit a website.
robots.txt follows the robots exclusion standard in order to ensure all users/scrapers can understand the file.
This is a screen shot of a part of the project Gutenberg robots.txt file. The line that says 'user-agent: *' means the following rules apply to all robots. The file paths that end with '/' means that they include all subgroups within that website path. This shows that project Gutenberg does not want to have its website scraped.
One of the main reasons why websites are against scraping as it causes a drain on the server. This means if scraping code is written to download books at intervals this may not create a problem for the website. Still, one should refer to the websites fair use policy and if possible contact the host.
Scraping against the terms of a website can have negative repercussions. This could include 'crawler traps', hidden in the website so that algorithms get caught out when trying to scrape. There may also be an IP blocker, that will stop a certain IP from accessing the website. This would be a large problem as we wouldn't be able to do any scraping (including manual scraping) if this were to occur.
One way to over come this issue is to use mirrors. Mirrors are static copies of the website stored elsewhere. Websites provide these to allow scraping without draining the main websites resources. Project Gutenberg has a number of mirrors which can be found at https://www.gutenberg.org/MIRRORS.ALL. Gutenberg also provides a how-to on mirroring from their website. This includes a recommendation to use rsync so this is what we have chosen to use. We used the mirror aleph.gutenberg.org.
rsync -av --exclude '*iso' --exclude '*ISO' --exclude '*png' --exclude '*PNG' --exclude '*jpg' --exclude '*JPG' --exclude '*xml' --exclude '*htm' --exclude '*html' --exclude '*mp3' --exclude '*mp4' --exclude '*m4b' --exclude '*ogg' --exclude '*spx' --exclude '*m4a' --exclude '*pdf' --exclude '*ly' --exclude '*midi' --exclude '*css' --exclude '*mid' --exclude '*sfv' --exclude '*doc' --exclude '*GIF' --exclude '*gif' --exclude '10802' --exclude '11220' --exclude '19159' aleph.gutenberg.org::gutenberg .
The code above was used in downloading the Gutenberg Corpus using rsync and the aleph.gutenberg .org mirror. It was typed into a cygwin command prompt that had rsync installed. It would also work on a Linux terminal with rsync installed. The “-av” section references the function to copy and paste all of the material in the mirror. The multiple 'excludes' exclude file types that are not necessary. The only necessary files types are .txt and folders. The “--exclude '10802' --exclude '11220' --exclude '19159'” section references folders in the mirror that have too many file types to filter and definitively have no useful text files. While an include statement would have been easier, there was a problem where some folders were excluded. In order to include all folders and text documents, the multitude of exclude statements are used.
When we first used rsync, we predicted the file size to small. There where many more files on the server than we originally accounted for. Gutenberg includes images, sound files and multiple copies of the same book indifferent file formats, this is why the rsync code was modified to include the multitude of 'excludes.' Even if we got rid of all the wrong file formats we would still have to deal with all the files that do not fulfill the projects requirements for processing. In the end we chose to filter out incorrect file types in our original rsync before then using Metadata to filter the files even further.
https://softwareengineering.stackexchange.com/questions/180108/what-will-happen-if-i-dont-follow-robots-txt-while-crawling https://www.gutenberg.org/robots.txt https://en.wikipedia.org/wiki/Robotsexclusionstandard