We start from a class of experiments that we want to define - e.g., DDoS experiments.

[ExDescLang]

=== Metadescriptions ===

The highest level is '''metadescription''' (Steve sometimes calls this '''model''') of that experiment class. It contains '''dimensions''' that are important to be defined for this class of experiments. Metadescriptions are created by experts in the given research area. Users usually don't touch them or if they do they start from an existing one and modify it. If there's no metadescription in a given field there should be a nice user-friendly process that lets experts create it from scratch by defining the required dimensions and then slowly add to it. Each dimension should allow for multiple choices and their combinations, e.g., multiple topologies connected together, multiple traffic streams, etc.

Every metadescription has the following dimensions:

 * topology (could or could not be domain-dependent. we move the domain-dependent part into invariants. for example "cong. control experiments need a common core where congestion occurs.) - LANGUAGE: TopDL with understanding that there's a way to translate this into NS
 * invariants (statements that must be true for this class of experiments to be valid, and conditions for this to happen. domain-specific) - LANGUAGE: Arun's DETERmine grammar ss final output but user may interact with a translation of it in English
 * actors are defined separately - actors map to topology somehow - there may be additional directives to denote how to do this mapping. For each actor you may choose to use one or many, or you could group them and use one or many actor groups in your experiment (e.g. simultaneous DDoS attacks) - LANGUAGE: TBD but pretty simple
 * event timeline (JTW calls this '''workflow''', domain-specific) - LANGUAGE: Arun's DETERmine grammar; 

Some metadescriptions contain more like: 

 * traffic (could be domain-specific, depending on type of traffic - mission vs background) - it's a little vague what portion of traffic gets defined in event timeline as opposed to here. We should have an option of defining multiple traffic streams at one place (here) if they are similar. Defining traffic means defining request/reply sizes, timing, content, etc. depending on the generator being used for this dimension. If event timeline mentioned specific traffic (e.g., DNS) then here we'd offer generators (JTW sometimes calls this '''models''') that can generate such traffic - for that particular event. In general we should offer here all generators since users may want to generate some background traffic that's noise in the experiment.  
 * visualization (domain-specific) - LANGUAGE: Pointers to tools, their inputs and outputs
 * post-processing (domain-specific) - LANGUAGE: Pointers to tools, their inputs and outputs
 * monitors (domain-specific) - LANGUAGE: Pointers to tools, their inputs and outputs
 * whatever else makes sense for that class of experiments

Each dimension can be output from multiple '''generators'''. A generator can be as abstract as an equation, or it could be an output of a simulation, or a set of data points, or pretty much anything else. Each generator can have '''constraints''' pretty much describing its inputs and outputs such as "this equation creates Internet-like topologies only when they contain more than 50 nodes". Each generator has an '''input''' set of variables and an '''output''' one where the output is in some common format (or translatable into it) for that dimension.

=== Experiment Design ===

User comes to the testbed with some research hypothesis - "my worm can spread to all vulnerable machines in the network in 10 seconds provided that fan in/out is at least 3". 

Starting from metadescription the system should be able to select a set of generators for each dimension that satisfy relevant invariants. These generators are shown as options to the user to choose from and parametrize. This interaction with the user is called '''experiment design''' (used to be '''template''' in June'10). Almost any choice should be coupled with a default value so that users can just accept defaults and run the experiment, while other users may decide to change the selection or parametrize it differently. During the design phase a user may decide they need another dimension or another generator for an existing dimension. These should then be added to the metadescription.

Making a selection for one dimension may reduce choices for other dimensions - this is where the system checks constraints against each other and against invariants and only keeps valid combinations around. 

=== Experiment Start ===

Based on user's choices the system generates the topology file and a '''set of scripts''' (SEER or others) that are directly runnable on the testbed (in June'10 we called this a '''recipe''').

=== Experiment Runtime ===

A '''validity monitor''' (experiment health) is always collecting data and making sure invariants hold. Users may define an empty workflow and experiment manually like now, or start with a workflow and manipulate it on the fly or start with a workflow and insert manual events into the stream. Once an invariant is violated we may or may not be able to tell the user exactly why this happened but we should be able to localize time/location where the failure occurred and provide logs for further analysis.

Any monitors selected by the user in the design stage are also running, as is any processing of that data and visualization.

=== Post Experiment ===

Any post-processing actions are performed, logs are collected and the set of scripts can be archived (with or without logs and experimental outputs) for future use.

=== TODO ===

What language is each of the dimensions described in. What I/O we need for each dimension.