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This is an early draft chapter from a forthcoming book on Zope, to be published by O'Reilly & Associates. The material has not been through O'Reilly's editorial process, nor has it been reviewed for technical accuracy. O'Reilly & Associates disclaims responsibility for any errors in this draft and advises readers to use the information contained herein with caution.

O'Reilly & Associates grants readers the right to read this material and to print copies or make electronic copies for their own use. O'Reilly & Associates does not grant anyone the right to use this material as part of a commercial product or to modify and distribute it. When O'Reilly & Associates publishes the final draft of this book in print form, the content will be made available under an open content license, but this chapter is not open content.

If you have any comments on the material in this chapter, you should send them to the authors, Michel Pelletier and Amos Latteier, at docs@digicool.com.

Preface

About This Book

This book is about Zope, the Open Source application server that is fundamentally changing the way people think about web information.

What Is Zope?

Like all good breakthrough software, defining Zope can sometimes be hard. We'll make it easy by starting with the cookbook definition.

Zope is an Open Source application server, focusing on content management, portals, and custom services. Zope specializes in rapid deployment of rich services to diverse audiences.

There are three key ideas in Zope: more power for more people, all tiers as managed content, and web components.

More Power For More People

Zope was originally designed for a newspaper business model, where the Zope customer (the ISP) had many customers (newspapers) that in turn had many customers (the newspaper customers). To scale in this environment, Zope had to embrace the idea safely delegating control at each stage to customers below you in the website.

Safely delegating control came to require many things. First, you had to present information in a way people could understand. Most people think of clicking on folders, not issuing SQL statements, so Zope got a hierarchical object database that felt like a filesystem. Giving crude, admin-intensive, command-line logins wouldn't work, so all of Zope became managed through a web browser. You don't want your customers to shoot you in the foot, so Zope got an undo facility to let people recover from any change they made.

These and innumerable other features made Zope a highly-differentiated environment for programming and authoring web content. Releasing Zope as Open Source provided the power for business decision makers to know they were in control of their technology decisions.

Thus, more power for more people is the key values statement for Zope.

All Tiers As Managed Content

Classic web applications have a common approach. For example, let's use the common "three tier" model, where an application has a presentation tier, a logic tier, and a data tier.

Most websites have the presentation material in one place on a filesystem, managed by one class of users. The logic is managed using other tools in another place on the filesystem. Finally, the data are managed in another place, usually a relational database server.

This model cleanly enforces the logical separation of tiers. However, it means there are three tools, two storage locations, two sets of user information, two facilities to cluster, etc. Worse, none of management of those three tiers is particularly web-friendly.

In Zope, all tiers are managed content that get a common set of services: security, web-based management, cataloging, workflow, clustering, syndication, etc. By representing all tiers as "objects" in the Zope framework, new models and consistent services can be applied.

All tiers as managed content is the architectural key idea in Zope, and is a tremendous differentiator.

Web Components

The Web is now the platform. That is, the web has evolved enough standards and APIs that creators of services, products, and technology can think in terms of the web as the architectural model.

Evidence of this is sprouting up in many locations. Microsoft's ".NET" architecture envisions a world of web components running on remote systems, providing specific services to any application in the world. People sitting in front of browser wouldn't be the only use of the web.

Tim O'Reilly also discusses this vision, posing the question "Should Amazon have an API?" In this model, a website allows itself to be used in ways never predicted beforehand by publishing connectors other programs can use in new ways.

Zope is uniquely positioned for this future model. In Zope, "programs" have URLs that can be used just as if the program was being run locally. The facilities used for this are the same standards in the vision of "web components".

This model of web components is the vision key idea for Zope. While the model is compelling and gathering steam, at this point it is still forward-looking.

Who Is Zope For?

It takes a lot of people working together to create web services:

Consumers use the site to locate and work with useful content.
Business Users create and manage content in the site.
Site Designers administer the look and feel.
Site Developers program the services in the site.
Administrators keep the software and environment for the site running.
Information Architects make the decision for the platform and keep track of the big picture.

Zope is a platform in which Site Developers create rich services to be turned over to Site Designers and Business Users.

As a platform, Zope can host Zope products that are focused on different audiences. For instance, Squishdot is a popular weblog, written in Zope, that is useful "right out of the box". Squishdot users might never realize Zope is underneath. Other Zope products, such as Digital Creations' content management system, take the same approach to covering audiences not targeted by Zope.

What Do You Need Zope for?

Dynamic Content: You want to your web site to tailor its presentation to its users, integrate information in databases and provide users with searching. You'd also like to make your web site automate and facilitate your business processes. Can your web site react intelligently to visitors to provide a compelling experience?
Web Site Management: A small web site is easy to manage, but a web site that serves thousands of documents, images and files needs to provide you with powerful management tools. Can you manage your site's data, business logic and presentation all in one place? Can you keep up with your content, or is it getting out of hand?
Security: When you deal with lots of web users, security becomes very important. It is crucial to organize users and be able to safely delegate tasks to them. For example folks in you engineering department need to be able to manage their web pages and business logic, designers need update site templates, and database administrators need to manage database queries. Can your system handle thousands of users, perhaps linked to your existing LDAP or other databases with flexible security rules?
Network Services: Right now most web sites serve users, but soon web sites will need to serve remote computer programs and other web sites. For example, you'd like to make your news items automatically available to wire service web sites. Or maybe you want to make products for sale on your site automatically searchable from a product comparison site. Can you leverage your existing data and business logic to create network services or will you have to start over from scratch?
Integration: Your content is strewn all over the place, relational databases, files, web sites, FTP archives, XML; can you unify your data into one coherent application? Does your system support web standards so that you can integrate content from legacy systems and new systems that you will add in the future?
Scalability: So you struck it rich and now your getting more hits then you ever imagined. Now you need to handle a thousands of times more traffic than before. Can you move your site to a different database and server platform and spread the load across multiple servers? Can your web site grow to handle your success?

What Zope Gives You

Management Environment: The first thing you'll notice about Zope is that it lets you manage your site's data, logic, and presentation right in your web browser. This means that Zope is easy to use and is remotely administrable. Zope lets you collaborate with others to interactively develop your web site.
Built in Tools: Zope comes with site management tools, a web server, a search engine, database connectivity, security and collaboration services, and more. Out of the box Zope gives you everything you need to build a powerful web site.
Standards Support: Zope excels at gluing together diverse data because of its support for open standards. Zope supports Internet
Open Source: With Zope you don't just get an application, you get the source and a community. Since Zope is open source you are not held hostage by a single vendor; your are free to use distribute and adapt Zope to fit your needs. Zope also benefits from an active user and developer community which improves Zope's support, audits Zope's security, fixes bugs, and adds features.
Extensibility: Zope can be extended in many directions. Third party applications can be easily created and distributed. The Zope community has produced hundreds of Zope add ons for everything from credit card processing to web discussions.

Zope History

In 1996 Jim Fulton, the CTO of Digital Creations, had to give a class on CGI programming. On the way back from the class, Jim considered what he didn't like about traditional CGI based programming environments. From these initial musings, Zope was born.

Jim and Digital Creations went on to release three open source software packages to support web publishing, Bobo, Document Templates, and BoboPOS. These three components have evolved into core components of Zope.

Back then, Digital Creations had developed a commercial application server based on their three open source components. This product was called Principia. Spurred by far-sighted investor Hadar Pedahazur, Digital Creations open sourced Principia in November 1998 and renamed it Zope.

Zope Community

Zope was one of the first tools of its kind to become open source. Since opening up the code to Zope, the user base has grown tremendously.

The Zope community consists of Zope users and developers. Many of the community members are professionals, investing their time and money into supporting Zope, others are just curious hackers, learning how to use a cool new tool. The community gets together occasionally at conferences but spends most of its time discussing Zope on the many Zope mailing lists and web sites.

How the Book Is Organized

Part I

Chapter 1: Using Zope: The first part of the book covers the most important Zope concepts and gets the reader up and running with Zope. By the end of this part the reader should be able to use Zope to create and manage simple but powerful web applications.
Chapter 2: Building Applications with Basic Objects: This chapter introduces "objects", which are the meat of Zope. It covers what an object is in general and then goes on to introduce the basic Zope objects: folders, DTML document, DTML method, file and image. It should stress examples of how to use Zope objects and how they work together to form basic applications.
Chapter 3: Dynamic Content and Scripting with DTML: This chapter introduces DTML, Zope's tag-based scripting language. It describes DTML's use for templating and scripting and its place in relation to other methods of scripting Zope. It covers DTML syntax and the three most basic tags, var, if and in.
Chapter 4: Security: This chapter looks at how Zope handles users, authentication, authorization, and other security related matters. Security is central to Zope's design and should be central to web applications that Zope users create.

Part II

Chapter 5: Advanced DTML Scripting: This chapter takes a closer look at DTML. It covers DTML security and the tricky issue of how variables are looked up in DTML. It also covers advanced uses of the basic tags covered in chapter 3 and the myriad special purpose tags.
Chapter 6: Scripting Zope: This chapter covers scripting Zope with more powerful tools than DTML. This chapter covers how to write business logic in Zope. It discusses the idea of methods in Zope, and focus on Python and Perl methods. It describes how to write Zope methods and covers method binding and security. Different methods (including DTML Methods) are contrasted.
Chapter 7: Relational Database Connectivity: This chapter describes how Zope connects to external relational databases. It covers the objects needed to connect to and query databases along with Zope's features which allow you to treat relational data like normal Zope objects. Also covered are security and performance considerations.
Chapter 8: Searching and Categorizing Your Zope Site: This chapter shows how to index and search objects with Zope's built-in search engine, the Catalog. It introduces indexing concepts and discusses different patterns for indexing and re-indexing. It covers using ZCatalog to index and search. Finally meta-data and search results are covered.

Part III

Chapter 9: Application Design: This chapter looks at Zope application design. It covers issues and solutions for building and maintaining large web applications. It focuses on issues of management and scalability.
Chapter 10: Extending Zope: This chapter covers extending Zope by creating your own classes of objects. The chapter does not cover Python Products. It discusses ZClasses, and how instances are built from classes. It describes step by step how to build a ZClass and the attendant security and design issues. Finally it briefly discusses creating Python base classes for ZClasses and describes the base classes that ship with Zope.

If you have any comments on the material in this chapter, you should send them to the authors, Michel Pelletier and Amos Latteier, at docs@digicool.com.