= Topdl Library =

This page describes the python library for manipulating topologies that follow the [TopDl topdl] model and are generally output in the topdl language.  It is broken up into a reference section describing the various python classes and procedures and an examples section.

= Reference =

== Installing and Accessing ==

The topdl library is available as oart of the DETER module of the DETER federation system.  Any system that has fedd installed will have topdl installed as well.  In particular, {{{users.isi.deterlab.net}}} has the library installed.

To install the library separately, follow the [FeddDownload#GitAccess instructions for getting fedd from git], make the distribution, and install the {{{deter-data-}}}''version''{{{.tar.gz}}} tar file using the [FeddDownload#DownloadingandInstallingthetarfile same procedure for installing the fedd tar file].  Installing all of fedd will work as well, of course.

Once the library is installed, python programs can access it by:

{{{
#!/usr/bin/env python

from deter import topdl
}}}

== The Classes ==

The class hierarchy mirrors the entities of the [TopDl topdl model].  Where the description of the model glosses over the details of the classes that parameterize the top-level abstractions, this reference will discuss them all.  Each of these classes is a python class, and can be created and manipulated independently, but in a proper topology they are grouped together.

A Substrate object has members that are Capacity and Latency objects.  This listing shows that nesting:

 * Substrate
   * Capacity (0 or 1)
   * Latency (0 or 1)
   * Attribute (0 or more)

The other common element, a Computer object, has the following nested objects:

 * [TopdlLibrary#ComputerClass Computer]
  * CPU (0 or more)
    * Attribute (0 or more)
  * !OperatingSystem (0 or more)
    * Attribute
  * Software (0 or more)
    * Attribute (0 or more)
  * Storage
    * Attribute
  * Interface (0 or more)
    * Capacity (0 or 1)
    * Latency (0 or 1)
    * Attribute (0 or more)
  * Service (0 or more)
    * !ServiceParam (0 or more)

Most classes can have attributes attached to them that contain extention attributes that different applications make use of.  The presence or absence of an optional nested object does not mean the presence or absence of the thing it describes, but that the description is unbound.  As [TopDl#Representation we have seen] a Computer without a nested CPU object does not describe a computer without a CPU, but a computer with no constraints on the CPU.
  
== Adaptive Constructors ==

The constructors of the various topdl classes will accept contained classes in several formats.  They will always accept an object of the relevant class.  They will also take a dict that maps constructor parameters to values for the given class.  Examples make this clearer than description.

The following calls to create a CPU object are equivalent:

{{{
cpu = topdl.CPU(type='Intel', attribute=[topdl.Attribute(attribute='clock_rate', value='1Ghz')])
}}}

and

{{{
cpu = topdl.CPU(type='Intel', attribute=[{'attribute': 'clock_rate', 'value': '1Ghz'}])
}}}


and 

{{{
cpu = topdl.CPU(**{'type': 'Intel', 'attribute' : [ {'attribute': 'clock_rate', 'value': '1Ghz'}]})
}}}

That is, inner class parameters can be specified using dicts directly, and a top level dict can user the standard ** operator.

All topdl class constructors take the member names as parameters, and should be called using named parameters, as above.  The only exception to this is the [TopdlLibrary#SubstrateObject Substrate object]'s {{{interfaces}}} member.

== Topdl Class Features ==

All topdl classes implement the following methods:

 {{{set_attribute(self, key, value)}}}::
   Attach an user-defined attribute with the given key and value to this object; value and key are strings.  The method includes a key/value pair (encoded as an [TopdlLibrary#Attribute attribute object]) into the {{{attribute}}} member of the object.  If an attribute with the given key exists, it is overwritten. 
   This method accesses the attribute member of the given object, not any named members. Objects that do not have an {{{attribute}}} member silently discard the operation.
 {{{get_attribute(self, key)}}}::
   Return the attribute of this object with the given key.  The attribute - a string - is returned.  If no such attribute exists, or the object has no {{{attribute}}} member, return None.
 {{{remove_attribute(self, key)}}}::
   If an attribute with the given key exists, remove it.
 {{{clone(self)}}}::
   Returns a deep copy of this object.
 {{{to_dict(self)}}}::
   Return the object as a python dict.  No copies are made, so make modifications with caution.
 {{{to_xml(self)}}}::
   Return the XML encoding (from the topdl language) of this object (and nested objects)

== Topology Class ==

This class holds an enitre topology.  The utility functions that read and write files operate on it, and it is generally the unit of I/O for the library.

It has the following members:

 {{{substrates}}}::
   A list of [TopdlLibrary#SubstrateClass Substrate objects] that contain the substrates of the topology.  The list may be empty indicating no communcations are possible.
 {{{elements}}}::
   A list of entities make up the network. These can be of any [TopdlLibrary#ComputerClass Computer objects], [TopdlLibrary#TestbedClass Testbed objects], [TopdlLibrary#SegmentClass Segment objects], or [TopdlLibrary#OtherClass Other objects]. The list may be empty indicating no elements are in the topology.
 {{{attribute}}}:::
   A list of [TopdlLibrary#AttributeObject Attribute objects] that are attached to the machine.  The list may be empty.
 {{{version}}}::
   The version of topdl that this object encodes.  

As usual, the constructor takes the member names as parameter names.

One useful specialized member is:

{{{
incorporate_elements(self)
}}}

That member sanity checks the substrates to make sure they are uniquely named, assigns names to any interfaces without them, and connects the {{{element}}} members of the [TopdlLibrary#InterfaceObject Interface objects].  If there are inconsistencies, it raises a {{{topdl.ConsistencyError}}} with more detail in the message.

{{{incorporate_elements()}}} is called by the {{{Topology}}} constructor as well and that constructor may throw the same exceptions.

== Computer Class ==

A Computer object is a programmable computer in a topology.  A webserver is well represented by a computer, as is a desktop.  
It has the following members:

 {{{name}}}::
   The unique name of the computer in the topology, a string.  Other names may be assigned in the {{{localname}}} attribute.
 {{{cpu}}}::
   A list of [TopdlLibrary#CPUObject CPU objects] that describe the CPUs of the machine.  The list may be empty, meaning no CPU requirements or information are present.
 {{{software}}}::
   A list of [TopdlLibrary#SoftwareObject Software objects] that describe the software to install.  The list may be empty, meaning no software is to be installed.
 {{{storage}}}::
    A list of [TopdlLibrary#StorageObject Storage objects] that describe the storage present the machine.  Storage objects can describe memory or persistent storage requirements.  The list may be empty, meaning no storage requirements or information are present.
 {{{interface}}}::
   A list of [TopdlLibrary#InterfaceObject Interface objects] that describe connections of the Computer to communications substrates.  The list may be empty, meaning that the computer is not connected to any substrates.
 {{{attribute}}}::
   A list of [TopdlLibrary#AttributeObject Attribute objects] that are attached to the machine.  The list may be empty.
 {{{localname}}}::
   A list of strings giving alternative names for the object.  When a machine is allocated to a testbed the DNS names assigned to the machine are given as {{{localname}}}s.  The list may be empty, meaning no such alternatives exist.
 {{{status}}}::
   A string indicating the current status of the Computer (if any).  It may also be None, indicating no status is reported.  Valid values are
     * "empty" - no allocation of resources has been attempted - generally not applied to Computers
     * "active" - Computer is functioning as part of an experiment
     * "inactive" - Computer is allocated, but not functioning
     * "starting" - Computer is transitioning from "inactive" to "active"
     * "terminating" - Computer is transitioning from "active" to "inactive"
     * "failed" - an allocation of resources has failed - generally not applied to Computers
 {{{service}}}::
   A list of [TopdlLibrary#ServiceObject Service objects] that describe the services this machine uses or supplies.  These are generally used by the federation system, and their definition is somewhat in flux. The list may be empty.
 {{{operation}}}::
   A list of strings that describe the valid operations on the machine.  These are generally used by the federation system, and their definition is somewhat in flux.The list may be empty.

The constructor takes the member names as parameters.  Only {{{name}}} is required.

A {{{Computer}}} should only be an element of one {{{Topology}}}.  Use {{{clone()}}} to avoid this.

== Substrate Object ==

The {{{Substrate}}} object represents a communication substrate.  The elements that have interfaces connected to a substrate can communicate with one another.  A {{{Substrate}}} may include default parameters for the latency and capacity of the communication channel.

The members are:

 {{{name}}}::
   A string, the unique name of the substrate.
 {{{capacity}}::
   A [TopdlLibrary#Capacity Capacity object] that gives the default capacity of the substrate.  It may be None, incdicating that there is no default.
 {{{latency}}::
   A [TopdlLibrary#Latency Latency object] that gives the default latency of the substrate.  It may be None, incdicating that there is no default.
 {{{attribute}}}::
   A list of [TopdlLibrary#AttributeObject Attribute objects] that are attached to the substrate.  The list may be empty.
 {{{localname}}}::
   A list of strings giving alternative names for the object.  The list may be empty, meaning no such alternatives exist.
 {{{status}}}::
   A string indicating the current status of the Computer (if any).  It may also be None, indicating no status is reported. Valid values are
     * "empty" - no allocation of resources has been attempted - generally not applied to Substrates
     * "active" - Substrate is functioning as part of an experiment
     * "inactive" - Substrate is allocated, but not functioning
     * "starting" - Substrate is transitioning from "inactive" to "active"
     * "terminating" - Substrate is transitioning from "active" to "inactive"
     * "failed" - an allocation of resources has failed - generally not applied to Substrates
 {{{service}}}::
   A list of [TopdlLibrary#ServiceObject Service objects] that describe the services this substrate uses or supplies.  These are generally used by the federation system, and their definition is somewhat in flux. The list may be empty.
 {{{operation}}}::
   A list of strings that describe the valid operations on the substrate.  These are generally used by the federation system, and their definition is somewhat in flux.The list may be empty. 
 {{{interfaces}}}::
   A list of [TopdlLibrary#InterfaceObject Interface objects] connected to this substrate.  The list may be empty, meaning that the substrate is not connected to any elements. This field is maintained by the [TopdlLibrary#TopologyObject Topology object] holding this Substrate object.  '''It is not a parameter to the constructor.'''

Other than {{{interfaces}}}, the constructor takes the member names as parameters.  Only the {{{name}}} is required.

Because the enclosing {{{Topology}}} object maintains the {{{interfaces}}} member, it is dangerous to have the same {{{Substrate}}} object in more than one {{{Topology}}}.  Use the {{{clone()}}} method to avoid this.


= Examples =