Welcome!

Industrial IoT Authors: Pat Romanski, William Schmarzo, Elizabeth White, Stackify Blog, Yeshim Deniz

Related Topics: Industrial IoT

Industrial IoT: Article

Use a Native XML Database for Your XML Data

Deciding when an XQuery-based native XML database is better than an SQL database

Developers tend to use the most familiar technologies. For data storage, that is the relational database. During design it's easy to see tables of data everywhere; however, not everything is relational in nature. When dealing with XML data or data easily expressed as XML, XQuery-based native XML databases (NXDs) present a viable and cost-effective alternative to relational databases, file system storage, or custom developed storage implementations. So, when is it time to consider an NXD?

Can native XML databases really provide a better answer for your data storage needs? In this article we'll examine some guidelines to help answer that question.

When to Consider a Native XML Database

  1. Do you have thousands of XML files?
  2. Is your XML data larger than 200MB?
  3. Are you trying to build a hierarchy into tables?
  4. Could your data change over time?
  5. Have you spent more that $100 on books explaining SQLXML?
The File System Isn't a Database
The first two questions are practical in nature. If estimates indicate more than 1000 XML files or 200MB of XML data exist, the file system isn't the right tool for the job. File systems are not built to manage large numbers of files in a single directory or huge directory hierarchies. Managing concurrency, out of disk space conditions, and other common problems will plague your application unless you use a database.

Naturally Hierarchical
The third reason to consider an NXD really has to do with the impedance mismatch between relational databases and XML data. Fundamentally, XML data is hierarchical and is a poor match for a relational database's rows and columns. Relational databases have always had a hard time modeling hierarchies. You'll find dozens of workarounds for this, but no real simple and efficient solution. Any XML-to-relational mapping tool will have to pick one of these techniques and manage this common case as best as possible. Regardless of the solution, performance will suffer. The end result will also be more brittle over time. Changing the structure of the data - which is easy, natural, and useful to do in XML - forces a redesign of the relational database and changes to the mapping layer. A single mapping mistake could completely skew an entire data set. As an XML document structure changes over time, it's possible for attributes to become elements, and vice versa. Over time, incremental changes to the logical structure of the XML data can force physical changes to the database, and wholesale dump and reload may be required of the relational system to keep pace.

Structured Yet Flexible Data
The fourth question suggests that requirements change over time, something true of most real world business systems. Once a relational database schema has been set in stone, only the database administrator (DBA) is qualified to change it without disrupting services. The contract between a relational database and the program that use it becomes the weakest link in the system. As requirements change, the DBA will spend endless hours mitigating the issues that arise. Contrast that with XML databases. XML is both structured and flexible. Even XML documents conforming to a DTD or XML Schema maintain a high degree of flexibility when compared to relational schemas. Most NXDs will optionally validate document structure. Even when document validation is not enforced, XML documents maintain a high degree of implicit structure. Therefore in either case, XML documents are flexible and structured and as a result the contract between the database and the programs using it is not brittle. It can withstand change without requiring a DBA.

Data Mapping Is Wasted Time, Money, and Effort
The last question is really a reality check. Take a second to consider the amount of time and money you've spent trying to make a solution workable. The best thing you can do when digging a hole is to stop digging and get out of the hole. With that in mind, let's look at SQLXML. If you need to mix and match SQL data and XML data, it's not a horrible way to go. However, if you view it as a way to squeeze XML into a relational system in which you've already invested, you might want to reconsider. You are going to pay a performance penalty for every document stored in terms of CPU and memory. Your ability to query, index, and optimize will be impacted as well. Executing XQuery against XML data mapped into relational tables will be hindered by the non-native storage format. An optimized native XML database won't have the same penalty.

Let's take a look at how to use an NXD to learn more about its advantages over a relational database.

Examples and Code
Berkeley DB XML is an open source XQuery implementation built atop the Berkeley DB transactional database system. It supports optimized XML storage, XQuery query planning, massive scale and concurrency, and is available for download as source code for multiple platforms and as a Windows installer from Sleepycat Software (www.sleepycat.com). Berkeley DB XML has also been integrated with Stylus Studio if you're more comfortable using an IDE for development. Berkeley DB XML is readily available to anyone, so we'll use it for the following examples.

First let's create an in-memory container for XML documents. Follow along using the "dbxml" command line provided with Berkeley DB XML.


dbxml> createContainer ""
dbxml> putDocument myDoc <names><name>joe</name><name>fred</
name><name>jane</name></names>
dbxml> query collection('')/names/name[.='joe']
dbxml> print
<name>joe</name>
Line 1 creates the container, while line 2 places a simple document into the container. The third line performs a query on the container returning each document that matches the XPath query /names/name[.=joe]. Finally it displays what we returned by the query statement.

That's all quite useful, but let's say that you need to access your XML storage programmatically. Because Berkeley DB XML is a library, and as such is linked into your application just as any other library would be, it does not incur the overhead of client/server communication. You interact with Berkeley DB XML using one of the supported language APIs. The primary one is C++, as the product is written in C++. Java, Python, Perl, PHP, and TCL are all supported API languages. Many other languages are supported by third parties and are readily available on the Internet.

With that in mind, let's next try some simple C++ code that calls for the same thing as the dbxml commands used in the previous example (see Listing 1).

The underlined sections of the code relate back to the first example. The first underlined section creates a container. This container is called 'test.dbxml,' and is on disk, and rather than in memory. The next underlined section places the same simple XML document into the new container. The last underlined section issues the query, and the while loop equates to the print statement. Put it all together and you have essentially the same result as before. In Java the code looks much the same; again the underlined areas are the common key sections of code (see Listing 2).

As you can see, the API is fairly straightforward and similar across languages. You'll note that the C++ and Java examples create a database on disk rather than in memory simply by giving the container a name.

Let's move back to the dbxml shell and try a more complicated example. This time let's add a few documents, so we can explore the performance of the system.

First let's populate an imaginary parts database.


dbxml> createContainer parts
Creating document storage container
That created an empty container and opened it as the default container in the shell. We can now use the putDocument command to run our XQuery and insert the sample data.

More Stories By Gregory Burd

Gregory Burd is the Product Manager for Sleepycat Software, now a part of Oracle. Prior to Sleepycat, he was on the business team at KnowNow, a Kleiner Perkins startup in the San Francisco Bay Area. He has many years of software development and product leadership within companies such as JavaSoft, a division of Sun Microsystems, Marble Associates, a consulting company, and NeXT Computer, now part of Apple Computer.

More Stories By Kimbro Staken

Kimbro Staken is an independent consultant, author, and open source developer specializing in technologies for XML data management. He is one of the primary developers of the dbXML Core Open Source native XML database and a cofounder of the XML:DB Initiative.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


IoT & Smart Cities Stories
Moroccanoil®, the global leader in oil-infused beauty, is thrilled to announce the NEW Moroccanoil Color Depositing Masks, a collection of dual-benefit hair masks that deposit pure pigments while providing the treatment benefits of a deep conditioning mask. The collection consists of seven curated shades for commitment-free, beautifully-colored hair that looks and feels healthy.
The textured-hair category is inarguably the hottest in the haircare space today. This has been driven by the proliferation of founder brands started by curly and coily consumers and savvy consumers who increasingly want products specifically for their texture type. This trend is underscored by the latest insights from NaturallyCurly's 2018 TextureTrends report, released today. According to the 2018 TextureTrends Report, more than 80 percent of women with curly and coily hair say they purcha...
The textured-hair category is inarguably the hottest in the haircare space today. This has been driven by the proliferation of founder brands started by curly and coily consumers and savvy consumers who increasingly want products specifically for their texture type. This trend is underscored by the latest insights from NaturallyCurly's 2018 TextureTrends report, released today. According to the 2018 TextureTrends Report, more than 80 percent of women with curly and coily hair say they purcha...
We all love the many benefits of natural plant oils, used as a deap treatment before shampooing, at home or at the beach, but is there an all-in-one solution for everyday intensive nutrition and modern styling?I am passionate about the benefits of natural extracts with tried-and-tested results, which I have used to develop my own brand (lemon for its acid ph, wheat germ for its fortifying action…). I wanted a product which combined caring and styling effects, and which could be used after shampo...
The platform combines the strengths of Singtel's extensive, intelligent network capabilities with Microsoft's cloud expertise to create a unique solution that sets new standards for IoT applications," said Mr Diomedes Kastanis, Head of IoT at Singtel. "Our solution provides speed, transparency and flexibility, paving the way for a more pervasive use of IoT to accelerate enterprises' digitalisation efforts. AI-powered intelligent connectivity over Microsoft Azure will be the fastest connected pat...
There are many examples of disruption in consumer space – Uber disrupting the cab industry, Airbnb disrupting the hospitality industry and so on; but have you wondered who is disrupting support and operations? AISERA helps make businesses and customers successful by offering consumer-like user experience for support and operations. We have built the world’s first AI-driven IT / HR / Cloud / Customer Support and Operations solution.
Codete accelerates their clients growth through technological expertise and experience. Codite team works with organizations to meet the challenges that digitalization presents. Their clients include digital start-ups as well as established enterprises in the IT industry. To stay competitive in a highly innovative IT industry, strong R&D departments and bold spin-off initiatives is a must. Codete Data Science and Software Architects teams help corporate clients to stay up to date with the mod...
At CloudEXPO Silicon Valley, June 24-26, 2019, Digital Transformation (DX) is a major focus with expanded DevOpsSUMMIT and FinTechEXPO programs within the DXWorldEXPO agenda. Successful transformation requires a laser focus on being data-driven and on using all the tools available that enable transformation if they plan to survive over the long term. A total of 88% of Fortune 500 companies from a generation ago are now out of business. Only 12% still survive. Similar percentages are found throug...
Druva is the global leader in Cloud Data Protection and Management, delivering the industry's first data management-as-a-service solution that aggregates data from endpoints, servers and cloud applications and leverages the public cloud to offer a single pane of glass to enable data protection, governance and intelligence-dramatically increasing the availability and visibility of business critical information, while reducing the risk, cost and complexity of managing and protecting it. Druva's...
BMC has unmatched experience in IT management, supporting 92 of the Forbes Global 100, and earning recognition as an ITSM Gartner Magic Quadrant Leader for five years running. Our solutions offer speed, agility, and efficiency to tackle business challenges in the areas of service management, automation, operations, and the mainframe.