DB2 XML最佳实践：提升数据管理效率与存储策略

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本文档主要探讨了IBM DB2 for Linux、Unix和Windows平台上的XML数据管理最佳实践。DB2 pure XML作为一个解决方案，旨在解决关系数据库模型中的问题，特别是在处理非结构化数据时提供了优势。本文涵盖了以下几个关键主题： 1. **XML的重要性与优缺点**：文章首先强调了XML在企业数据交换、Web服务和数据集成中的广泛应用，讨论了XML作为非结构化数据的优势（如易于共享和跨平台兼容性），同时也提及了与关系数据进行集成时可能遇到的挑战，如数据类型转换和查询性能。 2. **DB2 pure XML的优势**：DB2 pure XML相较于其他存储选项，提供了专门针对XML设计的高效存储和处理能力，有助于提高数据处理速度和查询性能。 3. **最佳实践概述**：作者分享了一系列针对DB2 pure XML的实用建议，包括选择合适的存储选项（如表空间类型和页大小）、优化XML数据的内联和压缩、以及如何高效地插入大型XML文档。 4. **示例场景**：文档以衍生交易的FpML格式为例，展示如何将这种XML数据有效地存储和管理在DB2中。 5. **数据存储策略**：讨论了针对XML数据的表空间选择，指出不同类型的表空间（如索引表空间或普通表空间）以及适合的页大小对性能的影响，并强调了混合存储方式（如将部分数据结构化）的可能性。 6. **XML数据质量控制**：在插入阶段，提到了如何确保XML数据的完整性，包括验证和清洗。 7. **查询效率**：探讨了SQL/XML与XQuery的比较，以及如何根据具体需求选择最有效的查询语言。还涉及如何有效地执行涉及XML的数据连接查询，正确使用星号(*)和双斜线(/)等操作符。本文档为DB2用户提供了深入理解和优化XML数据管理的具体指南，帮助他们充分利用DB2 pure XML的功能，提升数据处理和查询性能。无论是初次接触DB2纯XML还是寻求优化策略的用户，都能从中获益匪浅。

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Managing XML Data Page 13

predicate.

• Use a VARCHAR(n) index where the indexed character strings

have a maximum length of n, and the indexed elements are used

in range predicates (<, >).

• Use a VARCHAR HASHED index with elements or attributes

which will only be queried with equality predicates.

• Avoid defining indexes on non-leaf nodes. Index non-leaf nodes

only if it will clearly benefit expected query predicates and you

know the document structure well.

• Avoid using /text() in queries. A predicate with /text() can use an

index only if the index is also defined with /text().

• To allow index use with XML join queries, cast join predicates to

the type of the XML index.

Techniques for effectively maintaining and monitoring an XML

database:

• Use the runstats command with the EXCLUDING XML

COLUMNS clause to refresh only the relational statistics, if a

table contains relational and XML data.

• Use sampling with the runstats command to reduce the time for

executing the runstats command.

• Use the DB2 snapshot monitor to investigate the benefit of

different page sizes or other aspects of XML performance.

Techniques for developing efficient pureXML applications:

• Compile (“prepare”) very short database queries and pass

predicate literal values for each execution of the query to improve

total response time.

• Avoid code page conversion of XML data between DB2 and the

application to improve performance.

Managing XML Data Page 15

Summary” concludes with a summary of the most important guidelines.

Sample scenario: derivative trades in FpML format

A “derivative trade” is a financial trade which is based upon (derived from) some other

financial asset, such as a stock, an index, an interest rate, a currency, or other. In a

derivative trade, two parties agree to exchange cash, depending on market conditions

that affect the underlying asset. Typically, one party uses the trade to mitigate risk; the

other party uses the trade to gain immediate income (through fees or premiums) or to

speculate that future market conditions will provide profits. Consider the following

example.

YourWorld Investments and MyGlobal Bank agree on a currency exchange derivative

trade. They negotiate that on October 25, YourWorld will pay 71,900,000 Chinese Yuan to

MyGlobal, and MyGlobal will pay 10,000,000 US Dollars to YourWorld. MyGlobal will

profit from this trade if the value of the US Dollar declines below 7.19 CYN per USD

between now and Oct 25. MyGlobal might be using this trade to hedge against the risk of

a falling US Dollar. YourWorld might speculate that the US Dollar will gain in value, or

collect up-front fees from MyGlobal for entering the trade.

What’s interesting about derivatives is that (a) there are many different types and

variations, (b) the conditions of a particular trade are often individually negotiated and

complex, and (c) the life span of a derivative can range from days to years and their

conditions might change over time. The financial industry found that the flexibility and

extensibility of XML was required to define a standard data format that could capture the

high variability of derivatives. As a result, they developed FpML. FpML is essentially an

XML Schema that defines how XML elements and attributes are used to describe

derivative trades. The International Swaps and Derivatives Association, Inc (ISDA)

manages the FpML standard on behalf of a community of investment banks that make a

market in OTC derivatives. See [8] and [9] for more information on derivatives and

FpML.

Sample data and tables

Our sample database for this paper consists of three tables, shown in figure 1.

create table trades (tradeId integer, tradedoc XML);

create table parties(partyInfo XML);

create table currencies(symbol char(4), name varchar(30), USDvalue double,

lastUpdated timestamp);

Figure 1: Definitions of sample tables

All table definitions and commands to populate them with sample data as well as and

queries and other statements shown in this paper are available as a downloadable file at

http://www.ibm.com/developerworks/db2/bestpractices/.

The table TRADES contains FpML documents and a trade ID for each document. Each

trade document references the two trading parties using the values of their PARTYID

Managing XML Data Page 16

elements in the document. More detailed information about the parties is stored in XML

format in the PARTIES table. An XML-to-XML join between TRADES and PARTIES

allows us to find detailed party information for a given trade, or vice-versa. Many FpML

trades reference specific currencies by symbol. Additional currency information is

available in relational form in the CURRENCIES table, as shown in figure 2. We will need

XML-to-relational joins to relate trades to this currency information.

SYMBOL NAME USDVALUE LASTUPDATED

------ ------------------------------ -------- -------------------

USD US Dollar 1.000 2008-02-05-15.15.57

EUR Euro 1.460 2008-02-05-15.15.59

GBP Great Britain Pounds 1.960 2008-02-05-15.16.23

JPY Japanese Yen 0.009 2008-02-05-15.15.53

CNY Chinese Yuan (Renminbi, RMB) 7.190 2008-02-05-15.16.13

Figure 2: Content of the CURRENCIES table

Our PARTIES table contains 3 rows, with one XML document per row. They describe the

parties that are involved in the sample derivative trades. The following figure shows the

XML documents for the three parties.

<Party>

<Name>MyGlobal International Bank</Name>

<Status>Active</Status>

<Street>498 Wall Street</Street>

</Address>

</Rating>

</Party>

<Party>

<Name>National Village Bank</Name>

<Status>Active</Status>

<Street>1805 Back Street</Street>

<City>London</City>

</Address>

</Rating>

</Party>

<Party>

<Name>YourWorld Investments</Name>

<Status>Active</Status>

<City>Beijing</City>

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DB2 XML最佳实践：提升数据管理效率与存储策略

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