OPC【1】：重要名词解释

引言

OPC（Open Packaging Conventions）定义于“ISO/IEC 29500-2”文件。“ISO/IEC 29500” 包含4个文件，构成了Office Open XML标准。其中OPC定义了Package的读写规范。为了帮助继续学习OPC，此文档主要记录OPC中的重要概念。
 

basic

byte

sequence of 8 bits treated as a unit

Byte是字节，Bit是计算机二进制基本单位，Byte字节由8个Bits组成。

stream

linearly ordered sequence of bytes

线性有序的字节流。
 

abstract package model

Abstract model that defines abstract packages.
The abstract package model is a package abstraction that holds a collection of parts and relationships.

abstract package 是与physical package对应。

abstract package

logical entity that holds a collection of parts and relationships.

多个parts及relationships组成abstract package。可以将part看成abstrat package中的一个节点， relationship作为节点之间的一条边，abstract package存在一个虚拟的根节点。整个abstract package类似一个图数据结构。在docx第三方库中，docx.opc.part.Part的初始化定义：

class OpcPackage(object):
    """Main API class for |python-opc|.

    A new instance is constructed by calling the :meth:`open` class method with a path
    to a package file or file-like object containing one.
    """

    def __init__(self):
        super(OpcPackage, self).__init__()

part

stream with a name, a MIME media type and associated common properties.

对于part对象，需要指定在Package范围内唯一的名称，MIME类型——以便告知程序如何处理该part内容，以及part内存在的字节流stream。在docx第三方库中，docx.opc.part.Part的初始化定义：

class Part(object):
    """
    Base class for package parts. Provides common properties and methods, but
    intended to be subclassed in client code to implement specific part
    behaviors.
    """
    def __init__(self, partname, content_type, blob=None, package=None):
        super(Part, self).__init__()
        self._partname = partname
        self._content_type = content_type
        self._blob = blob
        self._package = package

source

part or package from which a connection is established by a relationship.

relationship关系边的起始端节点。该节点可以是part或者abstract package 虚拟根节点。

target

part or external resource to which a connection is established by a relationship.

relationship关系边的终止端节点。该节点可以是part节点或者外部资源。

relationship

package relationship or part relationship. package relationship is that connection from a package to a specific part in the same package, or to an external resource. part relationship is that connection from a part in a package to another part in the same package, or to an external
resource.

relationship将abstract package 中各个节点连接起来，使得用户可以通过虚拟根节点访问任意节点。docx.opc.rel._Relationship的初始化定义如下：

class _Relationship(object):
    """
    Value object for relationship to part.
    """
    def __init__(self, rId, reltype, target, baseURI, external=False):
        super(_Relationship, self).__init__()
        self._rId = rId
        self._reltype = reltype
        self._target = target
        self._baseURI = baseURI
        self._is_external = bool(external)

在abstract package中，每一relationship对象都具有唯一的rId及reltype。

relationship type

absolute IRI for specifying the role of a relationship.

相关的IRI定义于pack IRI。

IRI that conforms to the pack scheme.

pack scheme is that URI scheme that allows IRIs to be used as a uniform mechanism for addressing parts within a package.

Relationships part

part containing an XML representation of relationships.

relationships 的XML文件一般定义于“/_rels/.rels”文件中。
 

physical package model

physical format is specific file format, or other persistence or transport mechanism.

physical package is result of mapping an abstract package to a physical format.

physical package model 是将abstract package 按照指定的physical format要求，如docx格式——docx遵守zip标准，持久化到硬盘。

Media Types stream

stream in a physical package representing an XML document that specifies the media type
of each part in the package.

part的MIME类型一般定义于"/[Content_Types].xml”文件中。

 

参考资料

《Document description and processing languages — Office Open XML file formats》