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Introducing XAM Technology for Digital Curation

Learn about the eXtensible Access Method (XAM) standard, its benefits, practical examples, and opportunities for digital curation research.

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Introducing XAM Technology for Digital Curation

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  1. Presented by Paul McKeown (EMC) at the 4th Annual Digital Curation Conference December 3, 2008 Edinburgh, Scotland The eXtensible Access Method (XAM) Standardby Steve Todd (EMC)

  2. Purpose • This paper was written to introduce XAM technology to the Digital Curation community. • Agenda • Why XAM? • XAM Coding Example • Standards-based Digital Archives • Vendor plug-fest: Sun, EMC, and HP • Opportunities for Digital Curation Research

  3. Why XAM? • SNIA (Storage Networking Industry Association) • 100 Year Archive Survey • Key Problem: Logical and Physical Retention of Fixed Content • Logical: Data Formats • Physical: Migration to new Digital Archives • XAM Solution • Strong binding between content and meta-data • Vendor-neutral API for storing “fixed content objects” • Standards-based export-import between different vendors

  4. The XAM Approach • Location-independent Object naming • Each ‘Data Object’ (XSet) stored in XAM is assigned a globally unique name (a XUID). • These Location Independent Names allow data to migrate within or between XAM storage systems without impacting applications accessing the data. • Rich Metadata • XAM allows applications to bundle MIME-typed contextual metadata together with application data, facilitating easier data interchange among applications and longer “shelf life” for application data. • XAM provides for SQL like Query functionality • Pluggable Architecture for Storage System support • XAM Storage System vendors can plug their systems into the XAM API by creating a provider for the Vendor Interface Module API. • XAM also provides a standardized set of management disciplines and semantics for fixed content, such as retention, query, shredding etc.

  5. XAM Software Architecture Application ProgramISV / Custom XAM Toolkit API XAM Toolkit Library SNIA XAM API XAM API XAM API LibrarySNIA VIM API VIM API VIM Vendor A VIM Vendor B VIM Reference Vim - SNIA

  6. XAM Object Model • XAM defines 3 Primary Objects • XSet • Primary storage abstraction in XAM • Stores metadata and data in a collection of Fields • XSystem • Logical Container of XSets • Each XSystem Instance represents a connection with a particular XAM Storage System • XAM Library • Responsible for discovering and managing all VIMs in the XAM application environment • Provides Fields to report on and control global XAM attributes (API Revision Level, API Logging Level etc.) • Serves as a factory for XSystem Instances via Connect method

  7. XAM Primary Objects - XSystem • XSystem is an abstraction in the XAM API representing a logical container of XSets. • This is distinct from and possibly a subset/superset of the physical XAM Storage System. • An XSystem Instance combines an XSystem with an authenticated connection to one or more XAM Storage Systems. • An XSystem Instance is equivalent to a XAM Session. • In the XAM API, an XSystem Instance is created by calling XAM_Connect with a valid XRI (XSystem Resource Identifier). • XSystem instances are used to create, retrieve and delete XSets. • XSystem instances also have fields describing the system’s supported capabilities and management policies.

  8. XSet Fields XSet XAM Primary Objects - XSet • XSet – Addressable “Unit of Storage” in XAM Model • To store data in an XSystem an application must: • Create XSet Instance via XSystem • Create/Populate XSet fields with data • Commit the new XSet to persistent storage, saving resultant XUID Properties • “Simple” types (Boolean, Int, Float, String, DateTime, XUID) • - Type checked/enforced by storage system • Manipulated via “Property Get/Set” methods XStreams • Bytestreams, up to 2^64 bytes • Type assumed to be a valid MIME-type, but not checked/enforced by storage system • - Manipulated via Posix-style I/O methods (e.g., open, read, write, close)

  9. XSet Field ‘Binding’ Attribute • When a field is marked ‘Binding’ ( ) it means that this field’s value has a direct correspondence with this XSet’s XUID (the field’s value is relevant for the XSet’s identity) • ‘Non-Binding’ fields may be freely modified within the XSet, just as with traditional read/write storage • However, on an attempt to modify a ‘Binding’ field, the XSystem silently creates a completely new XSet, an identical copy of the original XSet, and assigns it a new XUID; the original XSet must be preserved under the original XUID • Applications are free to decide which XSet fields are ‘Binding’ at the time they are created XSet Fields XSet

  10. XUID – XSet Unique Identifier • XUID is the permanent name for an XSet • Assigned by XAM Storage System • XUIDs are Globally Unique • XUID Native format is binary sequence (10 – 80 bytes) • Base64 (RFC 2045) recommended for printable interchange • XSet’s XUID has a strict relationship with the XSet’s ‘Binding’ fields • If a ‘Binding’ field is modified, a new XSet with a new XUID is created upon commit • The old XSet is preserved as-is XUID Format

  11. XAM API XAM Write Example - Overview XAM 1.0 Application Program • Connect to XSystem • Create New XSet • Add XSet Metadata • Write XSet Data • Commit XSet • Release Resources XAM API Libraryxam.dll VIM API VIM example_vim.dll XSS Protocol XAM Storage System

  12. Storage System Application XAM API XAM Write Example – Connect to XSystem xam_string vXRI = “snia-xam://example_vim!10.1.1.1”; vStatus = XAMLibrary_Connect(vXRI,&vXSystem); XAMLibrary_Connect XAM Storage System10.1.1.1 XAM API Libraryxam.dll snia-xam://example_vim!10.1.1.1 VIM example_vim.dll

  13. XAM Connection Authentication • Once connected, an XSystem Instance must authenticate • XAM uses SASL Authentication Framework • Simple Authentication and Security Layer (RFC 4422) • PLAIN and ANONYMOUS methods always available • More advanced SASL methods (DIGEST-MD5, SECURID, KERBEROS-V5) advertised via XSystem property • .xsystem.auth.SASLmechanism.list.<mechanism> • PLAIN Authentication • “PLAIN\0\0<name>\0<secret>\0”

  14. Storage System Application XAM API XAM Write Example – Authenticate • authDataLength = BuildAuthBuffer(authBuffer,authName, authSecret); • vStatus = XSystem_Authenticate(vXSystem, authBuffer, authDataLength, &authStream); • XStream_Close(authStream); XSystem_Authenticate XAM Storage System10.1.1.1 XAM API Libraryxam.dll “PLAIN\0\0<name>\0<secret>\0” VIM example_vim.dll

  15. xset_handle vXSet; vStatus = XSystem_CreateXSet(vXSystem, XSET_MODE_MODIFY, &vXSet); Storage System Application XAM API XAM Write Example – Create XSet XSystem_CreateXSet XAM Storage System10.1.1.1 XAM API Libraryxam.dll XSET_MODE_MODIFY VIM example_vim.dll

  16. vStatus = XAM_CreateString(vXSet, “com.example.archive.invoice_id”, /* field name */ TRUE, /* binding */ vInvoiceID);/* value */ Storage System Application XAM API XAM Write Example – Add XSet Metadata XAMLibrary_Connect XAM Storage System10.1.1.1 XAM API Libraryxam.dll “com.example.archive.invoice_id” VIM example_vim.dll

  17. XAM Write Example – Write Binary Data • XAM stores binary data in special fields called Streams • Streams present POSIX-like write/read interface xstream_handle vXStream; vStatus = XAM_CreateXStream(vXSet, “com.example.archive.invoice_image",/* field name */ TRUE,/* binding */“image/tiff",/* MIME type */&vXStream); … Transfer Image Data ….vStatus = XStream_Close(vXStream); /* completes write*/

  18. XAM Write Example – Writing XStream Data • Transferring data from a file to an XStream do { /* Read data from file into buffer. */ vReadLength = fread(vDataBuffer, sizeof(char), BUFFER_SIZE,vInputFile); if (vReadLength > 0) { vPosition = 0; while (vPosition < vReadLength) { /* Write data from buffer to XStream. */ vStatus = XStream_Write(vXStream, &vDataBuffer[vPosition], vReadLength - vPosition, &vWriteLength); vPosition += vWriteLength; } /* Update accounting info */ vTotalWrite += vPosition; vTotalRead += vReadLength; } } while (vReadLength > 0);

  19. vStatus = XSet_Commit(vXSet, &vXUID); After Commit, application stores XUID return value permenently, for future XSet retrieval. Storage System Application XAM API XAM Write Content – Commit XSet XSet_Commit XAM Storage System10.1.1.1 XAM API Libraryxam.dll xset_handle VIM example_vim.dll

  20. XAM Write Content – Code Overview // Connect to XSystem vStatus = XAMLibrary_Connect(vXRI, &vXSystem); // XSystem Authentication vAuthDataLength = BuildAuthBuffer(vAuthBuffer, sAuthMethod, sAuthName, sAuthSecret); vStatus = XSystem_Authenticate(vXSystem, vAuthBuffer, vAuthDataLength,&vAuthStream); // Close auth stream vStatus = XStream_Close(vAuthStream); // Create XSet vStatus = XSystem_CreateXSet(vXSystem, XSET_MODE_MODIFY, &vXSet); // Add some identifying metadata vStatus = XAM_CreateInt(vXSet, PROPERTY(format_revision), true, 1); vStatus |= XAM_CreateString(vXSet, PROPERTY(invoice_id), true, vInvoiceID); vStatus |= XAM_CreateString(vXSet, PROPERTY(cust_id), true, vCustomerName)); // Write invoice image data using multiple threads and streams… vStatus = writeFileData(vXSet, vFilename, &vTotalBytes, &vSegmentCount); //Additional metadatavStatus = XAM_CreateInt(vXSet, PROPERTY(image_count), true, vSegmentCount); // Commit XSet vStatus = XSet_Commit(vXSet, &vXUID); // Display resulting XUID XUIDToString(vXUID, &vXUIDString); printf("Successfully wrote XSet, Base64 XUID:\n %s\n", vXUIDString);

  21. XAM Retention Model • Retention is the ability of an XSystem to prevent XSet deletion for an application-specified time period. • All XAM Retention policies have 3 primary aspects: • Enabled: Has the associated retention been turned on? • Duration:How long shall deletion be prevented (in milliseconds)? • Start Time: When does the retention clock start counting down? • XAM Base Retention • Start Time == XSet XUID Time • XAM Event Retention • Start Time is defined at some future date, triggered by business conditions • XAM Hold • “Freezes” an XSet until all holds are released

  22. Opportunities for Research • XAM provides a globally flat namespace. • Reduces management burden for configuring large digital archives (potentially no file systems, LUNs, or databases to configure) • XAM provides a location independent object model for data. • XUIDs are a form of persistent identifier; XAM places no limits on object counts. • XAM defines a canonical format for data migration. • Standardized data exchange format allows customers to migrate data from one system to another without engaging the applications that reference the data. • XAM provides a framework for coupling policy and other metadata together with data. • Archival Information Packages can be stored in one XSET and represented with one XUID.

  23. For Additional Information • SNIA XAM Initiative • XAMI home page - http://www.snia.org/forums/xam/ • XAM API specs -http://www.snia.org/forums/xam/specs • XAM Demo -http://www.snia.org/forums/xam/flshdemo/1282_SNIA_XAM.htm • SNIA Data Management Forum (DMF) • DMF home page - http://www.snia.org/forums/dmf/ • DMF Long Term Archive - http://www.snia.org/forums/dmf/programs/ltacsi/ • DMF 100 Year Survey - http://www.snia.org/forums/dmf/knowledge/100YrATF_Archive-Requirements-Survey_20070619.pdf • Steve Todd’s weblog • http://stevetodd.typepad.com/my_weblog/digital_preservation/ • http://stevetodd.typepad.com/my_weblog/centera/ • EMC Developer’s Network (Centera) • http://community.emc.com/community/edn/centera

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