Dean Arnold > DBD-Amazon > SQL::Amazon::UserGuide

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NAME ^

SQL::Amazon::UserGuide - User Guide for DBD/SQL::Amazon

SQL::Amazon SYNOPSIS ^

        #
        #       create the parser, passing in the current Amazon metadata
        #
        my $parser = SQL::Amazon::Parser->new(\%attrs);

        #
        #       parse a SQL statement, returning a SQL::Amazon::Statement
        #
        my $stmt = $parser->parse($sql_stmt)
                or die "Parse failed: " . $parser->errstr;
        #
        #       evaluate the parse tree, using an evaluation object
        #       for driver specific evaluation
        #       returns either a scalar rowcount for write operations,
        #               or a SQL::Amazon::Table object for SELECT
        #               or undef on error
        #
        my $results = $stmt->execute($params)
                or die "Evaluation failed: " . $stmt->errstr;

DESCRIPTION ^

SQL::Amazon provides the various components required by DBD::Amazon http://www.presicient.com/dbdamzn to query the Amazon E-Commerce Service 4.0 aka ECS using SQL.

Be advised this is ALPHA release software.

The suite includes the following components:

SQL::Amazon::Parser

provides SQL parsing and query plan generation. Implemented as a subclass of SQL::Parser, part of the SQL::Statement bundle.

SQL::Amazon::Statement

provides SQL query plan execution. Implemented as a subclass of SQL::Statement.

SQL::Amazon::Functions

provides SQL::Amazon-specific predicate functions, including MATCHES ANY, MATCHES ALL, MATCHES TEXT, POWER_SEARCH, IN, and NOT IN.

SQL::Amazon::ReqFactory

provides a factory class for generating SQL::Amazon::Request::Request objects based on the predicates in a query's WHERE clause.

SQL::Amazon::Spool

provides a temporary storage object for intermediate results extracted from the base table cache objects. Acts as a SQL::Eval::Table object for SQL::Statement processing.

SQL::Amazon::StorageEngine

provides a global storage engine for managing data caching and retrieval.

SQL::Amazon::Request::Request

provides a base class for all ECS request objects, including numerous default method implementations for building and sending requests, and processing the responses into the base table cache objects.

SQL::Amazon::Request::ItemLookup

a subclass of SQL::Amazon::Request::Request for the ItemLookup request; also acts as a base class for the ItemSearch request.

SQL::Amazon::Request::ItemSearch

a subclass of SQL::Amazon::Request::ItemLookup for the ItemSearch request

SQL::Amazon::Tables::Table

provides a base class for table cache objects, including methods for data type conversion, keyed lookup, and cache management.

SQL::Amazon::Tables::<tablename>

provides table-specific implementations of the Table base class.

Prerequisites

Perl 5.8.0

SQL::Statement 1.10

Clone 0.15

DBI 1.47

XML::Simple 2.09

LWP from of libwww-perl 5.803>

SQL Dialect

SQL::Amazon::Parser currently supports the same subset of standard SQL as supported by SQL::Statement, using the SQL::Dialects::Amazon dialect, with the following additional predicate functions for keyword searches:

MATCHES [ ANY | ALL | TEXT] (<keyword-list>)

Results in generation of an ECS ItemSearch request, with either the Keywords parameter (for MATCHES ALL), Power parameter (for MATCHES ANY), or TextStream parameter (for MATCHES TEXT).

POWER_SEARCH(<power-search-list>)

Results in generation of an ECS ItemSearch request, with either Power parameters. Individual items in the power-search-list are wrapped in parentheses, and joined with 'and' operators.

Special SQL Considerations

Mapping ECS Hierarchical Response Data to Relational Structures

The hierarchical structure of the data returned by the Amazon ECS requires some manipulation by SQL::Amazon to conform to a flattened relational model. As a result, queries against the Books table may cause multiple tables to be populated, e.g., Offers, CustomerReviews, EditorialReviews, ListManiaLists, etc. This behavior is especially true when the ResponseGroup parameter is set to Large (the default), in which case all detail information about matching books is returned.

As a result, some queries require the use of JOINs to properly reflect the data model abstraction. E.g., When searching for only New books, the Condition ECS request parameter must be applied; however, Condition is a column in the Offers table, not the Books table. Hence, a JOIN between the Books table and Offers table on the ASIN column is required, along with a predicate test for Offers.Condition = 'New'. The JOIN is required, even though the returned SELECT column list may not contain any Offers columns. Unfortunately, this requirement can have undesirable effects when the ResponseGroup parameter has been set to 'Small' or 'Medium' (via the DBD::Amazon amzn_resp_group attribute), as those response groups do not populate the Offers table. In that situation, SQL::Statement's eventual application of INNER JOIN logic will result in no JOIN'ed rows, and thus no results. In such cases, a LEFT JOIN may be required, and, due to limitations of the current SQL::Statement JOIN logic, the JOIN predicate must be placed within an ON clause aka, an EXPLICIT JOIN, rather than within the WHERE clause aka, an IMPLICIT JOIN.

"Pseudo" Columns

Another special consideration is the support for some "pseudo" columns within WHERE clauses that are not available for inclusion in the SELECT column list. These pseudo-columns are used to generate some ECS request parameters which do not have a direct element mappings in the ECS response data. The following pseudo-columns are currently available for predicates, but not the SELECT column list:

Subject - subject area fo the book; used for power searches
Language - the language of the book; used for power searches

Handling NULL Values for Request-mapped Columns

Under some circumstances usually when the ResponseGroup is set to 'Medium' or 'Small', some fields are not returned in the response, resulting in NULL values for those columns, which can create an issue for filtering the results in the WHERE clause, as NULL values in the usual comparison operators always evaluate to FALSE. While adding an "...OR <column> IS NULL..." predicate may seem a reasonable solution, the additional disjunction generated by this addition can result in extraneous ECS requests, thereby greatly increasing the processing time required. The best alternative in these cases is to create either a COALESCE() or DECODE() alias for the column in the SELECT returned column list.

Author Elements Combined Into a Single Authors Column

A single book item returned by ECS may include multiple Author elements. Rather than flattening these elements into a separate table, multiple Author elements are joined into a single string, using "; " as a separator, and placed in the Authors column of the Books table.

Cached Versions of Tables

SQL::Amazon maintains a cache of ECS results, keyed by the request identifier returned in each ECS response message. Normally, SQL::Amazon requires that a SELECT statement includes a WHERE clause that provides sufficient predicates to form an ECS request, in order to retrieve data on which the SELECT statement can further operate. In some instances, however, it may be desirable to use the existing data returned for a prior SELECT statement, e.g., to do further drill-down on the results of a prior SELECT during an ad-hoc query session. In support of this, alternate named tables, prefixed with the word "Cached", can be used to force the SELECT statement to operate only on the data currently in the cache for the specified table. E.g.,

        SELECT * FROM CachedBooks WHERE PublicationDate > '2002-01-01';

would return all the cached rows from Books with a PublicationDate > 2002-01-01, without issuing any further ECS requests.

Note that using cached tables may result in duplicate rows in the result set. Furthermore, due to the cache time limit requirements imposed by Amazon, rows may spoil out of the cache between consecutive references to a cached table.

Internals

Each statement handle created by DBD::Amazon http://www.presicient.com/dbdamzn creates its own SQL::Amazon::Statement object. All SQL::Amazon:Statement instances share a single SQL::Amazon::StorageEngine object, which manages the service request and table abstraction processing, and maintains the cache of previously retrieved results (subject to the Amazon ECS license's caching rules), in order to limit the number of requests required to satisfy a request.

ACKNOWLEDGEMENTS ^

Many thanks to Jeff Zucker for his assistance/guidance/patience on using, and accepting patches for, SQL::Statement.

FOR MORE INFO ^

http://www.presicient.com/dbdamzn

AUTHOR AND COPYRIGHT ^

Copyright (C) 2005 by Presicient Corporation, USA

mailto:darnold@presicient.com

http://www.presicient.com

Permission is granted to use this software according to the terms of the Artistic License, as specified in the Perl README file, with the exception that commercial redistribution, either electronic or via physical media, as either a standalone package, or incorporated into a third party product, requires prior written approval of the author.

This software is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Presicient Corp. reserves the right to provide support for this software to individual sites under a separate (possibly fee-based) agreement.

SEE ALSO ^

SQL::Statement for the supported SQL syntax, and how to subclass SQL::Parser.

DBD::Amazon http://www.presicient.com/dbdamzn for general usage instructions for the DBI interface to the Amazon ECS.

http://dbi.perl.org for general information on DBI

http://www.amazon.com/gp for information about the Amazon ECS API.

The DBI users mailing list mailto:dbi-users-subscribe@perl.org for help on the use of DBI.

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