Structure of ALTO files

Documentation

This document contains a listing of elements and their related attributes in ALTO version 2.0 with values or value sources where applicable. It is an "outline" of the schema, detailed by:

Root <alto> element
Top-level ALTO elements
    <Description> elements
    <Styles> elements
    <Layout> elements
ALTO attributes

ALTO requires use of the element as a child under the root element. The element requires use of a child element, which must carry a valid ID attribute value and a PHYSICAL_IMG_NR attribute value.

The 2.0 schema now has a target namespace URI: http://www.loc.gov/standards/alto/ns-v2#, to reflect that the standard is now maintained by the Library of Congress. The previous namespace URI reflected maintenance by CCS.

Root element in ALTO element set

alto

• Required: Yes.
• Usage: Root Element for bundling text layout technical metadata.
• Attributes: None.
• Contains AS SEQUENCE: Description, Styles, Layout.
• Contained by: None.

Top-level ALTO elements

These elements are direct children of the root element. The sorting is based on the accepted sequence in which they may be used.

Description

• Required: No.
• Usage: Describes general settings of the alto file like measurement units and metadata.
• Attributes: None.
• Contains AS SEQUENCE: MeasurementUnit, sourceImageInformation, OCRProcessing.
• Contained by: alto.

Styles

• Required: No.
• Usage: Styles define properties of layout elements. A style defined in a parent element is used as default style for all related children elements.
• Attributes: None.
• Contains AS SEQUENCE: TextStyle, ParagraphStyle.
• Contained by: alto.

Layout

• Required: Yes.
• Usage: The root Layout element.
• Attributes: STYLEREFS.
• Contains AS SEQUENCE: Page.
• Contained by: alto.

<Description> elements

These elements are contained by the element underneath . The sorting is based on the accepted sequence in which they may be used.

MeasurementUnit

• Required: No.
• Usage: All measurement values inside the alto file except fontsize are related to this unit. The default is 1/10 of mm.
• Attributes: none.
• Contains ENUMERATED VALUES: dpi, pixel, mm10, inch1200.
• Contained by: Description.

sourceImageInformation

• Required: No.
• Usage: Information to identify the image file from which the OCR text was created.
• Attributes: none.
• Contains SEQUENCE: fileName, fileIdentifier
• Contained by: Description.

OCRProcessing

• Required: No.
• Usage: Information on how the text was created, including preprocessing, OCR processing, and postprocessing steps. Where possible, this draws from MIX's change history.
• Attributes: ID.
• Contains: preProcessingStep, ocrProcessingStep, postProcessingStep
• Contained by: Description.

<Styles> elements

These elements are contained by the element underneath . The sorting is based on the accepted sequence in which they may be used.

TextStyle

• Required: No.
• Usage: A text style defines font properties of text.
• Attributes: ID, FONTWIDTH, FONTTYPE, FONTSTYLE, FONTFAMILY, FONTCOLOR, FONTSIZE.
• Contains: EMPTY ELEMENT.
• Contained by: Styles.

ParagraphStyle

• Required: No.
• Usage: A paragraph style defines formatting properties of text blocks.
• Attributes: ID, RIGHT, LEFT, ALIGN, LINESPACE, FIRSTLINE
• Contains: EMPTY ELEMENT.
• Contained by: Styles.

<Layout> elements

These elements are contained by the element underneath . The sorting is based on the accepted sequence in which they may be used.

Page

• Required: Yes.
• Usage: One page of a book or journal.
• Attributes: ID, PHYSICAL_IMG_NR, PRINTED_IMG_NR, PAGECLASS, PROCESSING, STYLEREFS, HEIGHT, WIDTH, QUALITY, POSITION.
• Contains SEQUENCE: TopMargin, LeftMargin, RightMargin, BottomMargin, PrintSpace
• Contained by: Layout.

textMD attributes

These attributes may appear on given elements within ALTO. The sorting is alphabetical.

ID

• Usage: A valid identifier as defined by the XML Schema specification.
• Contained by: OCRProcessing.

STYLEREFS

• Usage: To bind to IDREFs of various Text* elements.
• Contained by: Layout.