SchemaScanner

Produces a schema feature representing the feature type definition for each group of input data features.

Typical Uses

Generating a schema feature for dynamic writers
Generating schema features for comparison for schema validation and schema drift
Generating schemas after merging or manipulating datasets

How does it work?

The SchemaScanner receives features and determines their schema by scanning for attribute names and data types, based on the features' structure and attribute values.

It will scan either all features or a specified number of them, and can exclude certain attributes based on names, such as format-specific or internal FME attributes.

The resulting schema is output as a new schema feature, which has a specific form of list attribute and is output via the <Schema> port. It also receives a special attribute and value: fme_schema_handling = ‘schema_only’, which tells a dynamic writer to use that feature as a schema and then remove it from the output.

The original input features are passed out via the Output port.

The output order of the schema features relative to the data (input features) can be controlled using the Output Schema Before Data Features. For use with dynamic writers, the schema features should be output first.

Attribute Generation

Schemas can be generated with either standard data types or explicitly defined ones, according to the Numeric and String Data Types parameters:

Standard Types produces types such as fme_real64 , fme_int8 and fme_buffer.
Explicit Width and Precision produces types such as:
- fme_decimal(a,b) where a is the number of digits before a decimal, and b the number of digits after (precision).
- fme_varchar(a) where a is the maximum number of characters in a string.

When using Explicit Width and Precision, consider scanning all features (Number of Features to Scan) to ensure all existing attribute value lengths are considered.

Working with Dates

Dates and times may be optionally scanned for.

If strings match the FME datetime format of %Y%m%d%H%M%S they may be scanned for with Detect FME Dates .

To scan for strings that match another date or time format, use Convert Input Date Format to FME Date . Note that this option is only available if Output Schema Before Data Features is set to Yes.

See Standard FME Date/Time Format for formatting details.

Excluding Attributes

SchemaScanner processes all attributes on incoming features, including fme and format attributes. It is possible to ignore attributes using the Ignore Attributes Containing parameter.

Enter a regular expression, and matching attributes will be ignored.

For example, if the source data is CSV, you could use the regular expression ^fme_|^multi_|^csv_ to ignore any attributes starting with fme_, multi_, or csv_.

Schema Features

Schema features can be used to store or pass along schema structures - to dynamic writers, for example. The schema is stored in a list attribute named attribute, as shown here.

Each attribute has a name and an fme_data_type - note the attribute LAT has a corresponding data type of fme_real64.

Data types are FME internal data types.

Usage Notes

Schema features may also be generated manually, or by using the FeatureReader's schema options. Two readers also generate schemas - the Schema (Any Format) reader and the Schema (From Table) reader.
When using the SchemaScanner with a dynamic writer, the Output Schema Before Data Features parameter should be set to Yes, so that the schema arrives at the writer prior to the data features.

Configuration

Input Ports

Output Ports

Parameters

Group Processing

Group By

If Group By attributes are selected, features with the same values in the Group By attributes are grouped together, and one schema per group will be produced.

Complete Groups

Select the point in processing at which groups are processed:

When All Features Received	This is the default behavior. Processing will only occur in this transformer once all input is present.
When Group Changes (Advanced)	This transformer will process input groups in order. Changes of the value of the Group By parameter on the input stream will trigger processing on the currently accumulating group. This may improve overall speed (particularly with multiple, equally-sized groups), but could cause undesired behavior if input groups are not truly ordered.

General

Output Schema Before Data Features	Select an ordering option for the schema features: Yes (default): Schema features are output before their accompanying data features. Commonly used with dynamic writers. No: Schema features are output as they are completed.
Number of Features to Scan	Specify the number of features to scan to determine the dataset schema. If blank, all features are scanned. If this number is greater than the number of features received, all features are scanned. For very large datasets, setting this parameter may improve performance. The default is blank - scan all features.
Ignore Attributes Containing	Enter a regular expression. Attributes with matching names will be excluded from the schema.
Ignore Attributes	Select case sensitivity - Case Sensitive or Case Insensitive -for Ignore Attributes Containing regular expression matching.

Data Types

Numeric

Select the type of numeric value handling to be used in the schema:

Standard Types (such as fme_real64)
Explicit Width and Precision (such as fme_decimal(15,10))

String

Select the type of string value handling to be used in the schema:

Standard Types (such as fme_buffer)
Explicit Width and Precision (such as fme_varchar(7))

Missing/Null/Empty Attributes

Select a method for handling attributes without values:

Ignore
Use Default Data Type
Interpret Upstream Schema (Advanced)

Date Handling

Select a method for interpreting date and time strings.

Editing Transformer Parameters

Transformer parameters can be set by directly entering values, using expressions, or referencing other elements in the workspace such as attribute values or user parameters. Various editors and context menus are available to assist. To see what is available, click beside the applicable parameter.

How to Set Parameter Values

Defining Values

There are several ways to define a value for use in a Transformer. The simplest is to simply type in a value or string, which can include functions of various types such as attribute references, math and string functions, and workspace parameters.

Using the Text Editor

The Text Editor provides a convenient way to construct text strings (including regular expressions) from various data sources, such as attributes, parameters, and constants, where the result is used directly inside a parameter.

Text Editor

Using the Arithmetic Editor

The Arithmetic Editor provides a convenient way to construct math expressions from various data sources, such as attributes, parameters, and feature functions, where the result is used directly inside a parameter.

Arithmetic Editor

Conditional Values

Set values depending on one or more test conditions that either pass or fail.

Parameter Condition Definition Dialog

Content

Expressions and strings can include a number of functions, characters, parameters, and more.

When setting values - whether entered directly in a parameter or constructed using one of the editors - strings and expressions containing String, Math, Date/Time or FME Feature Functions will have those functions evaluated. Therefore, the names of these functions (in the form @<function_name>) should not be used as literal string values.

Content Types

String Functions	These functions manipulate and format strings.
Special Characters	A set of control characters is available in the Text Editor.
Math Functions	Math functions are available in both editors.
Date/Time Functions	Date and time functions are available in the Text Editor.
Math Operators	These operators are available in the Arithmetic Editor.
FME Feature Functions	These return primarily feature-specific values.
FME Parameters	FME and workspace-specific parameters may be used.
Creating and Modifying User Parameters	Create your own editable parameters.

Dialog Options - Tables

Table Tools

Transformers with table-style parameters have additional tools for populating and manipulating values.

Row Reordering

Enabled once you have clicked on a row item. Choices include:

Add a row
Remove a row
Move current row up one
Move current row down one
Move current row to top
Move current row to bottom

Cut, Copy, and Paste

Enabled once you have clicked on a row item. Choices include:

Cut a row - delete and copy to clipboard
Copy a row to the clipboard
Paste a row from the clipboard

Cut, copy, and paste may be used within a transformer, or between transformers.

Filter

Start typing a string, and the matrix will only display rows matching those characters. Searches all columns. This only affects the display of attributes within the transformer - it does not alter which attributes are output.

Import

Import populates the table with a set of new attributes read from a dataset. Specific application varies between transformers.

Reset/Refresh

Generally resets the table to its initial state, and may provide additional options to remove invalid entries. Behavior varies between transformers.

Note: Not all tools are available in all transformers.

For more information, see Transformer Parameter Menu Options.

Reference

Processing Behavior	Group-Based
Feature Holding	If Output Schema Features Before Data is Yes then the transformer will block all the incoming data features. This is usually required if you are using the schema feature with a dynamic writer. Target Number of Features to Scan will also block the data features - up to the number of features selected (or all features, if left blank).
Dependencies	None
Aliases
History

FME Community

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Search for all results about the SchemaScanner on the FME Community.

Examples may contain information licensed under the Open Government Licence – Vancouver, Open Government Licence - British Columbia, and/or Open Government Licence – Canada.

No Date Detection	Ignore dates.
Detect FME Dates (%Y%m%d%H%M%s$)	Detect datetime strings matching FME standard date/time format.
Convert Input Date Format to FME Date	When Output Schema Before Data Features is set to Yes, non-FME datetime formats may be detected and converted. Select a single format from the available options or enter a custom string. Note Output features may be altered (not only scanned) using this option, and so the schema must be output first. Consider using the Number of Features to Scan parameter to improve performance.