Add description of data model

docs/benchmarks-and-executions.md

+---
+title: Benchmarks and Executions
+has_children: false
+nav_order: 2
+---
+
+# Benchmarks and Executions
+
+In Theodolite, we distinguish between the static description of a scalability benchmark and its execution.
+
+## Benchmarks
+
+Benchmarks define what should be executed in scalability experiments. They
+consists of system under test (SUT) and an associated load generator, where
+both SUT and load generator are represented as sets of Kubernetes resources
+such Pods, Services, or ConfigMaps.
+Additionally, benchmarks define one or more load and resource types, scalability
+can be evaluated for.
+
+[TODO]: # (Link to metrics)
+
+Benchmarks are portable, that is they can be provided by standardization
+organizations, researchers, etc. and installed by other researchers,
+engineers, etc.
+They do not have a life-cycle. Instead, to run a benchmark, an execution of a
+benchmark is created and passed to Theodolite.
+
+## Execution
+
+An execution represents a one-time execution of a benchmark with a
+specific configuration. Hence, an execution refers to a benchmark and one of
+the load and resource types defined by that benchmark. Additionally, executions
+allow to alter the SUT or the load generator to evaluate regarding specific
+configurations.
+
+Executions also describe details regarding the scalability measurement method,
+such as for long experiment should be performed or how often they should be
+repeated.
+
+In contrast to benchmarks, execution have a life-cycle. They can be planned,
+executed, or aborted. Each execution of a benchmark is represented by an
+individual entity. This supports repeatability as executions can be archived
+and shared.