Ronald Bourret

Consulting, writing, and research in XML and databases

XML Database Products

Table of Contents

• 1.0 Introduction
• 1.1 XML and Databases
• 1.2 Product Categories
• 1.3 Terminology
• 1.4 Disclaimer
• 1.5 Copyrights, Trademarks, etc.
• 2.0 Product Index
• 2.1 Middleware
• 2.2 IDEs and Editors
• 2.3 XML-Enabled Databases
• 2.4 Native XML Databases
• 2.5 XML Servers
• 2.6 Wrappers
• 2.7 Content (Document) Management Systems
• 2.8 Discontinued Products
• 3.0 Related Products
• 3.1 XML Query Engines
• 3.2 XML Data Binding
• 4.0 Additional Links
• 5.0 Comments and Questions
• 5.1 Suggested Products

1.0 Introduction

In this Web page, I have tried to capture the current state of the market for XML database products. These are gathered from Web sites, product reviews, XML webzines, XML resource guides, and email from product users and developers.

1.1 XML and Databases

Although complete description of how to use XML with databases is beyond the scope of this page (see instead "XML and Databases"), a brief review will help you choose what product is right for you.

XML documents fall into two broad categories: data-centric and document-centric. Data-centric documents are those where XML is used as a data transport. They include sales orders, patient records, and scientific data. Their physical structure -- the order of sibling elements, whether data is stored in attributes or PCDATA-only elements, whether entities are used -- is often unimportant. A special case of data-centric documents is dynamic Web pages, such as online catalogs and address lists, which are constructed from known, regular sets of data. Document-centric documents are those in which XML is used for its SGML-like capabilities, such as in user's manuals, static Web pages, and marketing brochures. They are characterized by irregular structure and mixed content and their physical structure is important.

To store and retrieve the data in data-centric documents, what kind of software you need will depend on how well structured your data is. For highly structured data, such as the white pages in a telephone book, you will need an XML-enabled database that is tuned for data storage, such as a relational or object-oriented database, and some sort of data transfer software. This may be built in to the database (in which case the database is said to be XML-enabled) or might be third-party software, such as middleware or an XML server. If your data is semi-structured, such as the yellow pages in a telephone book or health data, you have two choices. You can try to fit your data into a well-structured database, such as a relational database, or you can store it in a native XML database, which is designed to handle semi-structured data. In addition, wrappers can treat an XML document as a source of relational data.

To store and retrieve document-centric documents, you will need a native XML database or content (document) management system. (Some XML-enabled databases provide native storage as well.) These are designed to store content fragments, such as procedures, chapters, and glossary entries, and may include document metadata, such as author names, revision dates, and document numbers. Content management systems generally have additional functionality, such as editors, version control, and workflow control. Although content management systems often use a native XML database for storage, this is hidden from the user.

1.2 Product Categories

I have divided products into the following categories. Please note that the boundaries between some of these categories are somewhat arbitrary.

• Middleware: Software you call from your application to transfer data between XML documents and databases. For data-centric applications.

• IDEs and Editors: Software designed to help you write XML applications or edit XML documents. For data-centric applications.

• XML-Enabled Databases: Databases with extensions for transferring data between XML documents and themselves. Primarily for data-centric applications.

• Native XML Databases: Databases that store XML in "native" form, generally as some variant of the DOM mapped to an underlying data store. This includes the category formerly known as persistent DOM (PDOM) implementations.For data- and document-centric applications.

• XML Servers: XML-aware J2EE servers, Web application servers, integration engines, and custom servers. Some of these are used to build distributed applications while others are used simply to publish XML documents to the Web. Includes the category formerly known as XML application servers. For data- and document-centric applications.

• Wrappers: Software that treats XML documents as a source of relational data. These products typically query XML documents using SQL. For data-centric applications.

• Content (Document) Management Systems: Applications built on top of native XML databases and/or the file system for content/document management. Include features such as check-in/check-out, versioning, and editors. For document-centric applications.

• XML Query Engines: Standalone engines that can query XML documents. For data- and document-centric applications.

• XML Data Binding: Products that can bind XML documents to objects. Some of these can also store/retrieve objects from the database. For data-centric applications.

• Discontinued products: Products that appear to be discontinued, since I can no longer find entries for them on the Web.

Except for content management systems, you will need to write code to integrate these products with your applications, although XML servers generally require more scripting and less code than the other categories. You will need to configure content management systems, which may be a non-trivial task in itself.

1.3 Terminology

The term template is described in section 5.2.1, "Template-Based Query Languages" of "XML and Databases". The terms table-based mapping and object-relational mapping are described in "Mapping DTDs to Databases".

1.4 Disclaimer

The product summaries in this Web site are not guaranteed to be complete, accurate, or up-to-date. You should use them as a starting point for your own research. Product summaries that have been written by the company are clearly labeled as "From the Web site" or "From the company". I have written all other summaries myself. I have not used any of these products except my own (XML-DBMS).

1.5 Copyrights, Trademarks, etc.

Quotes from Web sites and product descriptions written by companies are copyrighted by those companies. The remainder of this document is copyrighted by Ronald Bourret. Unless you specifically know otherwise, it should be assumed that all product and company names are trademarked by their owners.

2.0 Product Index

2.1 Middleware

2.2 IDEs and Editors

2.3 XML-Enabled Databases

2.4 Native XML Databases

2.5 XML Servers

2.6 Wrappers

2.7 Content (Document) Management Systems

2.8 Discontinued Products

3.0 Related Products

3.1 XML Query Engines

XML query engines are standalone programs that can query XML documents. Currently, these implement a variety of languages: XQL, XPath, XML-QL, Quilt, XQuery, etc. In the future, I expect most to standardize on the W3C query languages: XPath and XQuery.

The line between XML query engines and native XML databases is somewhat blurry, as native XML databases invariably support an XML query language. In general, XML query engines appear to support querying and nothing else, while native XML databases offer more database functionality: their own data store, transaction support, APIs, etc.

I have not had time to track XML query languages and their implementations. For more information about XML query languages, see:

• W3C's XQuery page. Includes news, mailing lists, a list of known XQuery implementations, the XQTS test suite, and links.

• XQuery Engines. List of XQuery implementations.

• XQuery.com. Various XQuery resources, including a tutorial, mailing list, product list, and the BumbleBee test harness.

• XML Query and Search Resources. List of XML query languages and other XML query resources. Last updated December, 2002.

Note that some middleware products and XML-enabled databases support XML query languages as well, although these generally support XML queries over back end data, rather than over XML documents themselves.

3.2 XML Data Binding

XML data binding is the binding of XML documents to objects designed especially for the data in those documents. This allows applications (usually data-centric) to manipulate data that has been serialized as XML in a way that is more natural than using the DOM. For a more complete explanation of XML data binding, as well as a list of products that support XML data binding, see:

• XML Data Binding Resources

4.0 Additional Links

For links to a variety of XML / database resources, including more software and papers about XML and databases, see the XML / Database Links page.

5.0 Comments and Questions

Please send comments and questions to me at rpbourret@rpbourret.com.

5.1 Suggested Products

If there is a product that you would like to see listed on this page, please send me information at the above email address. The only criteria for inclusion is that the product must be designed to let users store generic XML documents in or extract generic XML documents from databases. Products that only use XML internally or that severely restrict the XML that can be used -- such as to a single dialect -- do not qualify.

You are welcome to include a description of the product. This will help get your product listed faster, as I am always behind in researching/writing such descriptions. Your description will be clearly labeled as "From the company:" and I reserve the right to edit it. Any changes I make will be returned to you for technical review/approval.

Here are some guidelines to help you out:

• Audience. The intended audience is programmers.

• Technical detail. The purpose of the description is to give a concise technical description of the product: what it does, how it does it, and what features it has.

• Focus on XML. Focus on the XML aspects of the product, even if these took less time to write than that cool GUI tool. Mention the GUI tool in one sentence or less. ("Other features include ...")

• User tasks. Be sure to describe what the user must do. Writing code is different from filling in forms, both in terms of flexibility and difficulty.

• No vaporware. The features you describe must be in a released version of the product, not just in the specification or "under development".

• No marketing lingo. All marketing lingo will be deleted. Obvious examples of marketing terms are "enterprise-wide solution" and "business critical". Less obvious examples are such unverifiable terms as "fast", "scalable", and "robust".

• Still not sure what to write? Look at the descriptions of similar products in the list.