ALTO (Analyzed Layout and Text Object) is an open XML Schema developed by the EU-funded project called METAe.
The standard was initially developed for the description of text OCR and layout information of pages for digitized material. The goal was to describe the layout and text in a form to be able to reconstruct the original appearance based on the digitized information - similar to the approach of a lossless image saving operation.
ALTO is often used in combination with Metadata Encoding and Transmission Standard (METS) for the description of the whole digitized object and creation of references across the ALTO files, e.g. reading sequence description.
The standard is hosted by the Library of Congress since 2010 and maintained by the Editorial Board initialized at the same time.
In the time from the final version of the ALTO standard in June 2004 (version 1.0) ALTO was maintained by CCS CCS Content Conversion Specialists GmbH, Hamburg up to version 1.4.
The latest schema version and an overview about all versions with the links to the schema can be found at https://github.com/altoxml
An ALTO file consists of three major sections as children of the root <alto> element:
- <Description> section contains metadata about the ALTO file itself and processing information on how the file was created.
- <Styles> section contains the text and paragraph styles with their individual descriptions:
- <TextStyle> has font descriptions
- <ParagraphStyle> has paragraph descriptions, e.g. alignment information
- <Layout> section contains the content information. It is subdivided into <Page> elements.
<?xml version="1.0"?> <alto> <Description> <MeasurementUnit/> <sourceImageInformation/> <Processing/> </Description> <Styles> <TextStyle/> <ParagraphStyle/> </Styles> <Layout> <Page> <TopMargin/> <LeftMargin/> <RightMargin/> <BottomMargin/> <PrintSpace/> </Page> </Layout> </alto>
- Metadata Encoding and Transmission Standard (METS)
- Dublin Core, an ISO metadata standard
- Preservation Metadata: Implementation Strategies (PREMIS)
- Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH)