Hyppolyta - The Amazon Queen

Tags: projects

Do you strive to catalogue and sort your belongings? Do you own many books?

Hyppolyta is a rather elegant way to sort your books: Using the Amazon Webservices (AWS), you only need a barcode scanner, Perl, some CPAN modules and wget to gather information about all sorts of products: books, DVDs, CDs etc.

Sounds interesting? Read the article in my blog for more details or see below for the very detailed documentation.

You can find the program on my GitHub repository.

The Problem

I am an avid reader. In fact, most of the space in my shelves is used by books. Books that cover many different topics: Maths, Physics, Programming, Fantasy, Sci-Fi, Dramas/Plays, Poems, Classics…

Recently, I became aware of the fact that this collection had to be sorted and catalogued, somehow. This would enable me to sort out the duplicate books (A general problem when one has “some” books: One is given books by other people as a present, but most of them are already in the personal collection.) and prevent getting duplicates. Moreover, I said to myself:

If I catalogue all books that are stored somewhere in our house, I could easily spot the literary gems that are present in some dark box, unbeknownst to me and the others.

To solve this problem, several subproblems had to be taken care of: What book data do I need? How do I get this data? Where do I store the data? Thus, the problem was well-defined and I could begin looking for solutions.

A Solution

In Germany, most of the books that are published are assigned a unique number, the ISBN. On newer books, this number is printed on the back of the book as a barcode, allowing booksellers to get information (price etc.) about the book as quickly as possible.

For many years, the ISBN was a 10-digit number: 9 digits for the code itself and one for the checksum. However, since the beginning of 2007 (European) books are required to carry a 13-digit ISBN on their backs: The EAN. EAN is a much more general code that is, as the name implies, used for other product categories, such as DVDs, CDs or food.

Luckily (for me), the 13-digit ISBNs are a subset of the 13-digit EANs (Actually, the EAN comes in two flavours: 13 digit or 8 digits. The EAN-8 is commonly used for “smaller” items and since we are talking about catalogueing books and not about running a grocery store, I think we can gracefully ignore it.), so there would be no conversion necessary between these two codes.

Getting data

Quite naturally, the thought of how to exploit this fact came almost immediately to me. Given a list of EANs (I will now use this word regardless of whether I am writing about ISBNs or EANs.), I could get all the data I need if I had a source that allowed me to search for EANs and return information about the item.

Since I have not much money to spend on this project, I decided to query the most comprehensive (and free!) database of books I knew: The online bookstore “amazon.com”.

This task was easier than I expected it to be: amazon.com provides developers with (free) access to the “Amazon E-Commerce Service” (ECS). Being an amazon.com customer anyway, after reading the documentation, I decided to sign up for it and give it a try.

Getting EANs

Before doing anything else, I first had to find a way of how to read EANs. I was not willing to enter all EANs manually. But what was good for booksellers should work for me as well. So I bought an OVOX CCD-800 USB Barcode Scanner.

This device is truly perfectly suited for my needs: It reads EAN and UPC barcodes in all flavours (and a whole lot more barcodes which I will probably never encounter in my life) fast and reliably (if the barcode can be read, it will be read properly without any errors), it can be configured nicely (by scanning barcodes, of course, which is a mild case of bootstrapping if you ask me) and it identifies itself as a normal USB keyboard, hence allowing me to use it with FreeBSD (or Windows).

I configured the scanner to read the barcode, print it with alphanumeric characters and add a newline afterwards. This meant I could use vim, the best text editor, and scan every book I encountered. The EANs would be added to a list, which I would process later on.

Hyppolyta, the Amazon queen

After I knew what had to be done, I could begin implementing a program that would to the following:

  1. Accept a list of EANs as an input file.
  2. Request further information (Title, Author(s)…) via Amazon’s ECS.
  3. Save information about the items in a sensible and practical format.

The name “Hyppolyta” seemed very apt for this program.

Besides wondering how anyone could name a program “Hyppolyta”, you may have noticed that I wrote ‘items’ instead of ‘books’. This was a perfectly sane decision: Since amazon.com offers a lot more products besides books, I wanted my program to be as general as possible in order to get information about all sorts of products that can be identified by EANs. This resulted in me catalogueing my audio CDs and DVDs, too (but this is an entirely different story. Let’s focus here.).

Hyppolyta is written in Perl. With lots of modules and its general flexibility, this language seemed most suited for my task. Not to mention the fact that it is one of the languages that is officially supported by the ECS API.

I am by no means a Perl wizard. In fact, it was my first project that was done in Perl. I am sure that the code could be implemented much more smoothly, therefore I encourage you to rewrite it if you consider it too offensive.

The current version of Hyppolyta is able to generate CSV output. This simple format should allow you to use your data in almost any program. Just make sure that the program you are going to use for imports is able to understand CSV data that contains the newline character in fields! Every field is escaped by default via ".


Untar everything. Install wget and place it in the path of your Perl interpreter. Furthermore, install the following Perl modules, if not already present:

  • LWP::UserAgent
  • MIME::Base64
  • XML::XPath
  • Date::Format
  • Text::CSV_XS
  • Getopt::Long

As a last step, open hyppolyta.pl and look for the line:

my $req_key = "[YOUR KEY]"; 

Add your AWS access key. If you do not have one, please register with Amazon.

First steps

The steps of a general session with Hyppolyta could be something like this:

  1. Go through the shelves/boxes one by one. Scan all books you encounter. I suggest sorting them before starting to scan them. For example, I tend to group them in two categories, “technical literature” versus “fiction” and scan each category in a separate text file.
  2. You should now have a list of EANs/ISBNs. Each line does not contain any whitespaces and ends with a newline character. Start Hyppolyta from the command-line via:

    ./hyppolyta.pl -i <input file> -o <output file>.csv

    If you do not want Hyppolyta to download images for each item, specify the -n switch, too. Otherwise, all available images are stored in a subdirectory depending on the search index: If the search index is DVD, images will be stored in the folder ./dvd/. The URI of the image is set accordingly, thus allowing you to simply upload the appropriate folder to your server in order to display all DVDs. By default, wget is used to download the images.

  3. Hyppolyta will now download all information about the items and store them in a CSV file.

  4. Import the file and have fun. As always, this step is left out as an exercice to the reader.

More complex usages

To understand Hyppolyta’s configuration options you have to learn the basics about the “Amazon E-Commerce Service” (ECS). To get data from Amazon, an ItemLookup request is used. This request has several important parameters, which are preset by default when no other options are present:

  • The ReqEnd which specifies the locale. Set to de by default. You can change this via the -l or -locale switch:

    ./hyppolyta.pl -i <input file> --locale co.uk

    Valid locales are (among others): com, co.uk, de. Please note that not all locales share the same database. It is advisable to change the locale if an insufficient number of items has been retrieved.

  • The IDType that specifies the type of the search parameters, for example ISBN (default), UPC or EAN. Actually, more options are possible, but these are not covered here.

  • The ItemID, a list of up to 10 items of the type specified by IDType. These are, in fact, the codes you scanned earlier. The ID type can be changed using the -t or the --idtype switch:

    ./hyppolyta.pl -i upc.txt -t UPC

    Not all locales support all ID types. Read the fine manual for reference purposes.

  • The SearchIndex that tells Amazon which part of the catalogue is to be searched. Valid values include: Books, ForeignBooks, Music, DVD. The default value is “Books”. However this implies that only books of the request’s locale are queried! That means: If the locale is set to de (by default), books in other languages will be available only (!) by using the “ForeignBooks” search index. Specifying the search index is possible via the -s or --search-index switch:

    ./hyppolyta.pl -e -i classical_music.txt -s Music
  • The ResponseGroup, which used by Amazon to decide what information about an items is sent back. For example: The response group ItemAttributes returns a lot of information about each item, including package dimensions, whereas EditorialReviews adds the “official” review of the item to the response (if available). More information is available in the ECS documentation.

    This parameter should not be changed by the end user. Keep your hands off it unless you know what you are doing.

If available, as much as 10 items are used in one request. After the request has been assembled, it is sent to Amazon for processing. The response will be an XML file which is parsed by the XML::XPath module. This is where the heart of the program lies.

Tweaking Hyppolyta

To keep the program as general as possible, hashes are used everywhere in the program. If you look at the code, you will find two important variables: @attributes_general and %attributes_specific.

I will now explain to you how to use these wisely.


This is a list of attributes that have to be included in every request. Each item has two subitems: First, the title/name of the attribute is specified. Then, a relative path that tells Hyppolyta where the attribute can be found in the response (just think of a tree).

The name of the item is used when the CSV header is written. Although it is possible to use titles such as Item1, Item2 etc., it is not prudent as it makes parsing and understanding a CSV file much harder. You can change the names to your leisure.

The NodeIterate value tells Hyppolyta wich nodes are to be used to iterate over multiple items. In general, this is just the node of the attribute as described in the ECS documentation. It is also possible to add new attributes. Just make sure that the path to NodeIterate is correct.

The value in NodeValue tell Hyppolyta where it should look for the actual value you want to receive. This may be different from the NodeIterate setting.

Furthermore, specify the flag Output => 1 if you want Hyppolyta to print these values every time a new item has been retrieved from a request.

Example: Suppose we have a node called ‘Person’. This node has a child called ‘Name’. It it stored by ECS in the following way:

Person -- Name, Person -- Name, Person -- Name

In this case, we would set NodeIterate to ‘Person’ (actually, the whole path has to be used. But this is an example, after all) and NodeValue to ‘Name’.


An associative array for attributes that are only requested if a certain search index is used. The array’s key is the search index (keep in mind that ECS is indeed case-sensitive), the value is another hash of attributes that are requested for every item. The syntax is the same as above (Name, NodeIterate etc.).

While this may seem clumsy, it is, in fact, not, as I dare to say: People who want to organize their music collection need more information about artists etc., whereas people who want to sort their books are almost always happy to know about the author and the publisher.

If you want to add attributes, please read the ECS documentation for more information.

Use case: My collection

Let’s suppose you have your well-ordered list of ISBNs. Before doing anything else, these should be sorted according to their origin: In 13-digit ISBNs, the 4th digit will specify the origin: 4 is for Germany (or German-speaking countries), anything else for, well, another country. In 10-digit ISBNs, the origin is coded in the first number. Same game.

Use whatever you want to divide the list in two new lists (one with the “foreign” books and one with the local ones): Write a script, do it manually, use awk and sed etc.

At last, do two runs of Hyppolyta:

./hyppolyta.pl -i books_german.txt -o books_german.csv 
./hyppolyta.pl -i books_foreign.txt -s ForeignBooks -o books_foreign.csv

The .csv files now contain data about your books. Furthermore, images for every item available should have been downloaded.