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| Avro 1.1.0 API |
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| Avro is a data serialization system. |
| <P> |
| <B>See:</B> |
| <BR> |
| <A HREF="#overview_description"><B>Description</B></A> |
| <P> |
| |
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| <B>Packages</B></FONT></TH> |
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| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD WIDTH="20%"><B><A HREF="org/apache/avro/package-summary.html">org.apache.avro</A></B></TD> |
| <TD>Avro kernel classes.</TD> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD WIDTH="20%"><B><A HREF="org/apache/avro/file/package-summary.html">org.apache.avro.file</A></B></TD> |
| <TD>A container file for Avro data.</TD> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD WIDTH="20%"><B><A HREF="org/apache/avro/generic/package-summary.html">org.apache.avro.generic</A></B></TD> |
| <TD>A generic representation for Avro data.</TD> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD WIDTH="20%"><B><A HREF="org/apache/avro/io/package-summary.html">org.apache.avro.io</A></B></TD> |
| <TD>Input/output utilities.</TD> |
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| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD WIDTH="20%"><B><A HREF="org/apache/avro/io/parsing/package-summary.html">org.apache.avro.io.parsing</A></B></TD> |
| <TD>Implementation of Avro schemas as LL(1) grammars.</TD> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD WIDTH="20%"><B><A HREF="org/apache/avro/ipc/package-summary.html">org.apache.avro.ipc</A></B></TD> |
| <TD>Support for inter-process calls.</TD> |
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| <TD WIDTH="20%"><B><A HREF="org/apache/avro/reflect/package-summary.html">org.apache.avro.reflect</A></B></TD> |
| <TD>Use Java reflection to generate schemas and protocols for existing classes.</TD> |
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| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD WIDTH="20%"><B><A HREF="org/apache/avro/specific/package-summary.html">org.apache.avro.specific</A></B></TD> |
| <TD>Generate specific Java classes for schemas and protocols</i>.</TD> |
| </TR> |
| <TR BGCOLOR="white" CLASS="TableRowColor"> |
| <TD WIDTH="20%"><B><A HREF="org/apache/avro/util/package-summary.html">org.apache.avro.util</A></B></TD> |
| <TD>Common utility classes.</TD> |
| </TR> |
| </TABLE> |
| |
| <P> |
| <A NAME="overview_description"><!-- --></A> |
| <P> |
| Avro is a data serialization system. |
| |
| <h2>Overview</h2> |
| |
| <p>Avro provides: |
| <ul> |
| <li>Rich data structures. |
| <li>A compact, fast, binary data format. |
| <li>A container file, to store persistent data. |
| <li>Remote procedure call (RPC). |
| <li>Simple integration with dynamic languages. Code generation |
| is not required to read or write data files nor to use or |
| implement RPC protocols. Code generation as an optional |
| optimization, only worth implementing for statically typed |
| languages. |
| </ul> |
| |
| <h2>Schemas</h2> |
| |
| <p>Avro relies on <i><A HREF="org/apache/avro/Schema.html" title="class in org.apache.avro"><CODE>schemas</CODE></A></i>. |
| When Avro data is read, the schema used when writing it is always |
| present. This permits each datum to be written with no per-value |
| overheads, making serialization both fast and small. This also |
| facilitates use with dynamic, scripting languages, since data, |
| together with its schema, is fully self-describing. |
| |
| <p>When Avro data is stored in a <A HREF="org/apache/avro/file/DataFileWriter.html" title="class in org.apache.avro.file"><CODE>file</CODE></A>, its schema is stored with |
| it, so that files may be processed later by any program. If the |
| program reading the data expects a different schema this can be |
| easily resolved, since both schemas are present. |
| |
| <p>When Avro is used in <A HREF="org/apache/avro/ipc/package-summary.html"><CODE>RPC</CODE></A>, the client |
| and server exchange schemas in the connection handshake. (This |
| can be optimized so that, for most calls, no schemas are actually |
| transmitted.) Since both client and server both have the other's |
| full schema, correspondence between same named fields, missing |
| fields, extra fields, etc. can all be easily resolved. |
| |
| <p>Avro schemas are defined with |
| with <a href="http://www.json.org/">JSON</a> . This facilitates |
| implementation in languages that already have JSON libraries. |
| |
| <h2>Comparison with other systems</h2> |
| |
| Avro provides functionality similar to systems such |
| as <a href="http://incubator.apache.org/thrift/">Thrift</a>, |
| <a href="http://code.google.com/protobuf/">Protocol Buffers</a>, |
| etc. Avro differs from these systems in the following fundamental |
| aspects. |
| <ul> |
| <li><i>Dynamic typing</i>: Avro does not require that code be |
| generated. Data is always accompanied by a schema that permits |
| full processing of that data without code generation, static |
| datatypes, etc. This facilitates construction of generic |
| data-processing systems and languages. |
| <li><i>Untagged data</i>: Since the schema is present when data is |
| read, considerably less type information need be encoded with |
| data, resulting in smaller serialization size.</li> |
| <li><i>No manually-assigned field IDs</i>: When a schema changes, |
| both the old and new schema are always present when processing |
| data, so differences may be resolved symbolically, using field |
| names. |
| </ul> |
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