pyBeamline

pyBeamline is a Python version of Beamline. While the same set of ideas and principles of Beamline have been ported into pyBeamline, the underlying goal and technology are very different.

pyBeamline is based on ReactiveX and its Python binding RxPY. RxPY is a library for composing asynchronous and event-based programs using observable sequences and pipable query operators in Python. Using pyBeamline it is possible to inject process mining operators into the computation.

A complete Jupyter notebook presenting all implemented techniques is available at https://github.com/beamline/pybeamline/blob/master/tutorial.ipynb.

Goals and differences with Beamline

The main difference between Beamline and pyBeamline is the language they are built in (Beamline is written in Java, pyBeamline is written in Python). However, differences do not stop here. In particular, Beamline is built on top of Apache Flink, which makes it suitable for extremely efficient computation due to the distributed and stateful nature of its components. pyBeamline, on the other end, is built on top of ReactiveX which is

an extension of the observer pattern to support sequences of data and/or events and adds operators that allow you to compose sequences together declaratively while abstracting away concerns about things like low-level threading, synchronization, thread-safety, concurrent data structures, and non-blocking I/O. (From https://reactivex.io/intro.html)

Therefore, pyBeamline is suited for prototyping algorithm very quickly, without necessarily bothering with performance aspects. In a sense, it simplifies the construction of proof of concepts, before translating the algorithms into Beamline for proper testing and verification. Also, it simplifies collaboration by, for example, leveraging online services (like Google Colab).

To give an example of such simplicity, this is the complete code to discover a DFG using a sliding window from a stream generated from a test.xes file (a file is used instead of a proper stream, as we are in a very controlled setting):

from pybeamline.sources import xes_log_source_from_file
from pybeamline.mappers import sliding_window_to_log
from reactivex.operators import window_with_count
from pm4py import discover_dfg_typed

xes_log_source_from_file("test.xes").pipe(
    window_with_count(6),
    sliding_window_to_log()
).subscribe(lambda log: print(discover_dfg_typed(log)))

Differences with PM4PY

PM4PY has a package dedicated to streaming algorithms. This package, however, does not allow the construction of the dataflow for the processing of the events. Instead, it allows the application of a single algorithm on a defined stream. While this might be useful in certain situation, having the ability to construct the dataflow represents a fundamental architecture for stream processing.

Installing the library

To use pyBeamline on any OS, install it using pip:

pip install pybeamline

Basic concepts

In this section the basic concepts of pyBeamline are presented.

Events

The pyBeamline framework comes with its own definition of event, called BEvent, similarly to what is defined in Beamline. Here some of the corresponding methods are highlighted:

Essentially, a Beamline event, consists of 3 maps for attributes referring to the process, to the trace, and to the event itself. While it's possible to set all the attributes individually, some convenience methods are proposed as well, such as getTraceName which returns the name of the trace (i.e., the case id). Internally, a BEvent stores the basic information using as attribute names the same provided by the standard extension of OpenXES. Additionally, setters for attributes defined in the context of OpenXES are provided too, thus providing some level of interoperability between the platforms.

Observables and Sources

An observer subscribes to an Observable. Then that observer reacts to whatever item or sequence of items the Observable emits. This pattern facilitates concurrent operations because it does not need to block while waiting for the Observable to emit objects, but instead it creates a sentry in the form of an observer that stands ready to react appropriately at whatever future time the Observable does so. -- Text from https://reactivex.io/documentation/observable.html.

In the context of Beamline it is possible to define observables of any type. The framework comes with some observables already defined. Sources already implemented are xes_log_source, xes_log_source_from_file, and string_test_source. A xes_log_source creates a source from a static log (useful for testing purposes), xes_log_source_from_file creates a source from an XES file, and string_test_source allows the definition of simple log directly in its constructor (useful for testing purposes).

import pm4py
from pybeamline.sources import xes_log_source

xes_log_source(pm4py.read_xes("test.xes")) \
    .subscribe(lambda x: print(str(x)))

import pm4py
from pybeamline.sources import xes_log_source_from_file

xes_log_source_from_file("test.xes") \
    .subscribe(lambda x: print(str(x)))

from pybeamline.sources import string_test_source

string_test_source(["ABC", "ACB", "EFG"]) \
    .subscribe(lambda x: print(str(x)))

from pybeamline.sources import mqttxes_source

mqttxes_source('broker.mqtt.cool', 1883, 'base/topic/') \
    .subscribe(lambda x: print(str(x)))

input()

For convenience, another source called log_source is defined. This just combines dispatches the call to the other sources, based on a match performed on the input type.

log_source("test.xes") # This is equivalent to xes_log_source_from_file("test.xes")

log = pm4py.read_xes("test.xes")
log_source(log) # This is equivalent to xes_log_source(log)

log_source(["ABC", "ACB", "EFG"]) # This is equivalent to string_test_source(["ABC", "ACB", "EFG"])

Combining sources

In order to build tests where drifts occur in a controlled setting, it is possible to concatenate different sources together. See the example below:

from reactivex import concat
from pybeamline.sources import xes_log_source_from_file, log_source

src1 = xes_log_source_from_file("tests/log.xes")
src2 = log_source(["ABCD", "ABCD"])
src3 = xes_log_source_from_file("tests/log.xes")

concat = concat(src1, src2, src3)
concat \
    .subscribe(lambda x: print(str(x)))

Filters

The filter operator, in ReactiveX, does not change the stream, but filters the events so that only those passing a predicate test can pass. In Beamline there are some filters already implemented that can be used as follows:

from pybeamline.sources import log_source
from pybeamline.filters import excludes_activity_filter, retains_activity_filter

log_source(["ABC", "ACB", "EFG"]).pipe(
    excludes_activity_filter("A"),
    retains_activity_filter("G")
).subscribe(lambda x: print(str(x)))

Filters can operate on event attributes or trace attributes and the following are currently available:

from pybeamline.sources import log_source
from pybeamline.filters import retains_on_event_attribute_equal_filter

log_source("test.xes").pipe(
    retains_on_event_attribute_equal_filter("event-attrib", ["ev", "ab"]),
).subscribe(lambda x: print(str(x)))

from pybeamline.sources import log_source
from pybeamline.filters import excludes_on_event_attribute_equal_filter

log_source("test.xes").pipe(
    excludes_on_event_attribute_equal_filter("event-attrib", ["ev", "ab"]),
).subscribe(lambda x: print(str(x)))

from pybeamline.sources import log_sourcelog_source
from pybeamline.filters import retains_on_trace_attribute_equal_filter

log_source("test.xes").pipe(
    retains_on_trace_attribute_equal_filter("trace-attrib", ["tv", "ab"]),
).subscribe(lambda x: print(str(x)))

from pybeamline.sources import log_source
from pybeamline.filters import excludes_on_trace_attribute_equal_filter

log_source("test.xes").pipe(
    excludes_on_trace_attribute_equal_filter("trace-attrib", ["tv", "ab"]),
).subscribe(lambda x: print(str(x)))

from pybeamline.sources import log_source
from pybeamline.filters import retains_activity_filter

log_source(["ABC", "ACB", "EFG"]).pipe(
    retains_activity_filter("G")
).subscribe(lambda x: print(str(x)))

from pybeamline.sources import log_source
from pybeamline.filters import excludes_activity_filter

log_source(["ABC", "ACB", "EFG"]).pipe(
    excludes_activity_filter("A"),
).subscribe(lambda x: print(str(x)))

Please note that filters can be chained together in order to achieve the desired result.

Mappers and mining algorithms

pyBeamline comes with some mining algorithms, which are essentially instantiations of map and flatMap operators. This section reports some detail on these.

Discovery techniques

In the core of the pyBeamline library, currently, there is only one mining algorithm implemented:

from pybeamline.sources import log_source
from pybeamline.mappers import infinite_size_directly_follows_mapper

log_source(["ABC", "ACB"]).pipe(
    infinite_size_directly_follows_mapper()
).subscribe(lambda x: print(str(x)))

('A', 'B')
('B', 'C')
('A', 'C')
('C', 'B')

from pybeamline.algorithms.discovery import heuristics_miner_lossy_counting

log_source(["ABCD", "ABCD"]).pipe(
    heuristics_miner_lossy_counting(model_update_frequency=4)
).subscribe(lambda x: print(str(x)))

{'A': (node:A connections:{B:[0.5]}), 'B': (node:B connections:{C:[0.5]}), 'C': (node:C connections:{})}
{'C': (node:C connections:{D:[0.5]}), 'D': (node:D connections:{}), 'A': (node:A connections:{B:[0.6666666666666666]}), 'B': (node:B connections:{C:[0.6666666666666666]})}

from pybeamline.algorithms.discovery import heuristics_miner_lossy_counting_budget

log_source(["ABCD", "ABCD"]).pipe(
    heuristics_miner_lossy_counting_budget(model_update_frequency=4)
).subscribe(lambda x: print(str(x)))

{'A': (node:A connections:{B:[0.5]}), 'B': (node:B connections:{C:[0.5]}), 'C': (node:C connections:{D:[0.5]}), 'D': (node:D connections:{})}
{'A': (node:A connections:{B:[0.6666666666666666]}), 'B': (node:B connections:{C:[0.6666666666666666]}), 'C': (node:C connections:{D:[0.6666666666666666]}), 'D': (node:D connections:{})}

Conformance checking techniques

Currently only conformance checking using behavioral profiles is supported.

from pybeamline.algorithms.conformance import mine_behavioral_model_from_stream, behavioral_conformance

source = log_source(["ABCD", "ABCD"])
reference_model = mine_behavioral_model_from_stream(source)
print(reference_model)

log_source(["ABCD", "ABCD"]).pipe(
    excludes_activity_filter("A"),
    behavioral_conformance(reference_model)
).subscribe(lambda x: print(str(x)))

([('A', 'B'), ('B', 'C'), ('C', 'D')], {('A', 'B'): (0, 0), ('B', 'C'): (1, 1), ('C', 'D'): (2, 2)}, {('A', 'B'): 2, ('B', 'C'): 1, ('C', 'D'): 0})
(1.0, 0.5, 1)
(1.0, 1.0, 1)
(1.0, 0.5, 1)
(1.0, 1.0, 1)

Windowing techniques

ReactiveX comes with a very rich set of windowing operators that can be fully reused in pyBeamline. Applying a windowing techniques allows the reusage of offline algorithms (for example implemented in PM4PY) as each window is converted into a Pandas DataFrame.

To transform the window into a DataFrame, the sliding_window_to_log operators need to be piped to the source.

from pybeamline.sources import log_source
from pybeamline.mappers import sliding_window_to_log
from reactivex.operators import window_with_count
import pm4py

def mine(log):
    print(pm4py.discover_dfg_typed(x))

log_source(["ABC", "ABD"]).pipe(
    window_with_count(3),
    sliding_window_to_log()
).subscribe(mine)

Counter({('A', 'B'): 1, ('B', 'C'): 1})
Counter({('A', 'B'): 1, ('B', 'D'): 1})

Counter({('A', 'B'): 2, ('B', 'C'): 1, ('B', 'D'): 1})

Integration with other libraries

River

River (https://riverml.xyz/) is a library to build online machine learning models. Such models operate on data streams. River includes several online machine learning algorithms that can be used for several tasks, including classification, regression, anomaly detection, time series forecasting, etc. The ideology behind River is to be a generic machine learning which allows to perform these tasks in a streaming manner. Indeed, many batch machine learning algorithms have online equivalents. Note that River also supports some more basic tasks. For instance, you might just want to calculate a running average of a data stream.

It is possible to integrate pyBeamline's result into River to leverage its ML capabilities. For example, let's say we want to use concept drift detection using the ADWIN algorithm. In particular, we are interested in computing if the frequency of the directly follows relation BC changes over time. To accomplish this task, let's first build a log where we artificially inject two of such drifts:

import random

log_original = ["ABCD"]*10000 + ["ACBD"]*500
random.shuffle(log_original)

log_after_drift = ["ABCD"]*500 + ["ACBD"]*10000
random.shuffle(log_after_drift)

log_with_drift = log_source(log_original + log_after_drift + log_original)

After that we can use the capabilities of pyBeamline and reactivex to construct a pipeline that produce a sequence of frequencies corresponding to the frequency of directly follows relation BC in window with length 40 (which is chosen as all our traces have length 4). Also note that we leverage the fact that in all our events when B and C appear they are always in the same trace (because of how log_source generates the observable). We will later define a function check_for_drift:

import reactivex
from reactivex import operators as ops

log_with_drift.pipe(
  ops.buffer_with_count(40),
  ops.flat_map(lambda events: reactivex.from_iterable(events).pipe(
      ops.pairwise(),
      ops.filter(lambda x: x[0].get_trace_name() == x[1].get_trace_name() and x[0].get_event_name() == "B" and x[1].get_event_name() == "C"),
      ops.count()
      )
  )
).subscribe(lambda x: print(x))

from reactivex import operators as ops
from river import drift

drift_detector = drift.ADWIN()
data = []
drifts = []

def check_for_drift():
  index = 0

  def _process(x):
    nonlocal index
    drift_detector.update(x)
    index = index + 1
    if drift_detector.drift_detected:
      drifts.append(index)

  def _check_for_drift(obs):
    return obs.pipe(ops.do_action(lambda value: _process(value)))

  return _check_for_drift

For a complete working example, see https://github.com/beamline/pybeamline/blob/master/tutorial.ipynb.

Citation

Please, cite this work as:

• Andrea Burattin. "Beamline: A comprehensive toolkit for research and development of streaming process mining". In Software Impacts, vol. 17 (2023).