INTRODUCTION

A fundamental construct for using data in any number of electronic environments, whether they are databases, models, or the World Wide Web, is to have an understanding of the data or information that make up its essential parts. Metadata is literally the "data about data." Metadata is the information used by a variety of groups to design, create, describe, preserve, and use information resources and systems. The crucial, non pesticide specific elements of each Pesticide Root Zone Model (PRZM) field and orchard scenario is recorded as a means of preserving an authoritative and reproducible record of the design, construct, and source of each element of the scenario.

In general, the information assembled to created each scenario will have three basic features:

• content,
• context, and
• structure;

all of which are reflected through metadata. The data content relates to what each scenario contains or is about and is intrinsic to the field or orchard being modeled. Content reflects the element by which the designer authenticates and completes the content of the field or orchard scenario. For example, content is the date of a crop's maturation, the organic content of a particular soil, or the rate at which snow melts in the location of the scenario. Contexts are those aspects associated with the scenario's creation, such as the how or from where the soil characteristics were selected, where the weather station is located, or what cropping practices were chosen and why. The structure relates to the associations within and among the individual parameters that make up the scenario. An example of the structure would be the relationship of the depth of the total soil profile to the individual soil horizons. All three aspects of metadata are essential components of a scenario and have been captured and described in following pages.

In short, in an environment where immediate access to underlying information used to govern the construct of a PRZM field or orchard scenario, metadata:

• certifies the authenticity and degree of completeness of the scenario's content;
• establishes and documents the context of the scenario's content;
• identifies the structural relationships that exist between and within a parameter of the scenario;
• provides an access point for a diverse range of users of the scenario; and
• assembles electronically the information the developer might have ordinarily provided in a physical reference.

The following descriptions of each PRZM field and orchard scenario used in the assessment of drinking water exposures derived from surface water sources reflect the basic principles of establishing administrative and descriptive "metadata." However, it remains vitally important to understand that metadata is the "data about the data" and acting as umbrellas to this information are the established Agency procedures for ensuring the quality of that information. This is accomplished through the basic tenants of Quality Assurance and Quality Control in the selection of parameters that constitutes the field and orchard scenario.

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