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32 of 35 people found the following review helpful:
2.0 out of 5 stars
Does the basics., December 5, 2007
This review is from: Webbots, Spiders, and Screen Scrapers: A Guide to Developing Internet Agents with PHP/CURL (Paperback)
"Webbots, Spiders, adn Screen Scrapers" is a solid book for building basic scripts to do web scraping. Michael Schrenk goes covers the "should you do this" aspect very well, and devotes much of the book to these kinds of topics. On that reason alone I give him major kudos, "just because you CAN do a thing, doesn't mean you SHOULD."
Technically the book and examples are very basic and beginner level. All code is procedural and has absolutely no references to object oriented programming at all. This is great for a simple project, but building anything larger than a targetted webbot or two is beyond the scope of this book.
I was very dismayed at Mr. Schrenk's opinion of regular expressions:
"The use of regular expressions is a parsing language in itself, and most modern programming languages support aspects of regular expressions. In the right hands, regular expressions are also useful for parsing and substituting text; however, they are famous for thier sharp learning curve and cryptic syntax. I avoid regular expressions whenever possible."
This disregard for regular expressions effectively wipes out a powerful toolset for budding developers. Regular expressions are no harder to learn than PHP. The reasons for his disdain for them is also flawed:
"The regular expression engine used by PHP is not as efficient as engines used in other languages, and is certainly less efficient than PHP's built-in functions for parsing HTML."
PHP uses the same regular expression engine used (very effectively) in PERL with the use of the preg_* functions. There has been many studies that show preg_* style expressions outperform basic text matching in PHP. In this assesment the author is terribly wrong.
The book does a great job of explaining how to make single use scripts for scraping, but never how to create a larger infrastructure. There is no focus on creating multi process engines with pcntl_fork(), or proc_open(), these are critical for scaling web scraping applications. A single script scraping a few hundred websites on a single thread would take ages over a multi-threaded engine.
If you are looking to break into web scraping and not sure where to start, this is likely the best (and possibly only) book on the market. If you are intermediate or advanced you will quickly question the author's logic and see that scaling will become the number one issue you have to over come.
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24 of 26 people found the following review helpful:
3.0 out of 5 stars
Solid introduction to webbots, with a catch., April 27, 2007
This review is from: Webbots, Spiders, and Screen Scrapers: A Guide to Developing Internet Agents with PHP/CURL (Paperback)
I picked up this book full of enthusiasm, spiders are just plain cool, they go out and start downloading data for you, reading webpages, and even understanding them a little. My enthusiasm was dashed a little however on page four: You may use any of the scripts in this book for your own personal use, as long as you agree not to redistribute them... and agree not to sell or create derivative products under any circumstances.. I develop in PHP professionally, and a lot of the code I write ends up getting used somewhere with some sort of a for-profit basis, which pretty effectively prevents me from using any code between the covers (at its strictest reading, Im not sure I can even change the code).
The book does a great job of introducing different sorts of web agents that you can create programatically (more than just spiders) and introduces all sorts of interesting projects along those lines. Throughout the book a series of libraries written by the author are leveraged to make the retrieval and parsing of the various pages much easier. While newer developers will enjoy being able to concentrate on the big picture I found myself itching for more information on the nitty gritty.
Some of the projects explored include: price monitoring, image capturing (want to be your own google image search? :) ), link verification, spiders, and snipers. Each of the different projects received its own chapter, and effectively covered a lot of the topics covered within.
Overall, I would recommend this book to beginner to intermediate PHP developers looking to tackle the world of web agents, its a good primer on the related topics, and at the very least will give you some ideas on the complexities involved. As their skill grows they will probably find them-self either moving past the libraries included with the book, or modifying them greatly. My biggest complaint is the lack of coverage on the robots.txt file, some talk is given to it in terms of blocking robots from your own site, but I didnt see any code that actually dealt with parsing it for your own robot.
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9 of 9 people found the following review helpful:
5.0 out of 5 stars
Great Book with Lots of Information, August 25, 2007
This review is from: Webbots, Spiders, and Screen Scrapers: A Guide to Developing Internet Agents with PHP/CURL (Paperback)
This book covers every aspect I could ever hope a book on web bots would cover. It goes into great detail and provides lots of background information about things such as why you should use web bots, security issues, how to authenticate a bot with password protected sites, writing search engine crawlers, parsing HTML, how to handle cookies, HTTP headers, dealing with forms and a lot more.
I was very pleased with how this book covered concepts. The book uses PHP and the cURL library as a teaching tool instead of trying to give a lesson in how to use PHP as a crawler language. The way the code is explained makes it very easy to translate into whatever language you are most comfortable coding in. The book uses fundamental functional programming concepts which make it easy to pick up the general idea without actually knowing PHP.
My boss bought this book to help my group us with a project we were working on, and even my co-workers who had no background with PHP were able to use this book to write a web bot in C# (using the cURL library) very easily. The concepts from this book easily transfered over to object-oriented concepts.
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