The METS schema is a standard for encoding descriptive, administrative, and structural metadata regarding objects within a digital library, expressed using the XML schema language of the World Wide Web Consortium. The standard is maintained in the Network Development and MARC Standards Office of the Library of Congress, and is being developed as an initiative of the Digital Library Federation.

ALTO stores layout information and OCR recognized text of pages of any kind of printed documents like books, journals and newspapers. ALTO is a standardized XML format to store layout and content information. It is designed to be used as an extension schema for use with the Library of Congress' Metadata Encoding and Transmission Schema (METS) XML Schema, where METS provides metadata and structural information while ALTO contains content and physical information.

ALTO Introduction

ALTO Technical Information

XML Schema Definition

ALTO Reference Links