# Theory Inference

chapter‹EFSM Inference›
text‹This chapter presents the definitions necessary for EFSM inference by state-merging.›

section‹Inference by State-Merging›
text‹This theory sets out the key definitions for the inference of EFSMs from system traces.›

theory Inference
imports
Subsumption
"Extended_Finite_State_Machines.Transition_Lexorder"
"HOL-Library.Product_Lexorder"
begin

declare One_nat_def [simp del]

subsection‹Transition Identifiers›

text‹We first need to define the \texttt{iEFSM} data type which assigns each transition a unique identity.
This is necessary because transitions may not occur uniquely in an EFSM. Assigning transitions a unique
identifier enables us to look up the origin and destination states of transitions without having to
pass them around in the inference functions.›

type_synonym tid = nat
type_synonym tids = "tid list"
type_synonym iEFSM = "(tids × (cfstate × cfstate) × transition) fset"

definition origin :: "tids ⇒ iEFSM ⇒ nat" where
"origin uid t = fst (fst (snd (fthe_elem (ffilter (λx. set uid ⊆ set (fst x)) t))))"

definition dest :: "tids ⇒ iEFSM ⇒ nat" where
"dest uid t = snd (fst (snd (fthe_elem (ffilter (λx. set uid ⊆ set (fst x)) t))))"

definition get_by_id :: "iEFSM ⇒ tid ⇒ transition" where
"get_by_id e uid = (snd ∘ snd) (fthe_elem (ffilter (λ(tids, _). uid ∈ set tids) e))"

definition get_by_ids :: "iEFSM ⇒ tids ⇒ transition" where
"get_by_ids e uid = (snd ∘ snd) (fthe_elem (ffilter (λ(tids, _). set uid ⊆ set tids) e))"

definition uids :: "iEFSM ⇒ nat fset" where
"uids e = ffUnion (fimage (fset_of_list ∘ fst) e)"

definition max_uid :: "iEFSM ⇒ nat option" where
"max_uid e = (let uids = uids e in if uids = {||} then None else Some (fMax uids))"

definition tm :: "iEFSM ⇒ transition_matrix" where
"tm e = fimage snd e"

definition all_regs :: "iEFSM ⇒ nat set" where
"all_regs e = EFSM.all_regs (tm e)"

definition max_reg :: "iEFSM ⇒ nat option" where
"max_reg e = EFSM.max_reg (tm e)"

definition "max_reg_total e = (case max_reg e of None ⇒ 0 | Some r ⇒ r)"

definition max_output :: "iEFSM ⇒ nat" where
"max_output e = EFSM.max_output (tm e)"

definition max_int :: "iEFSM ⇒ int" where
"max_int e = EFSM.max_int (tm e)"

definition S :: "iEFSM ⇒ nat fset" where
"S m = (fimage (λ(uid, (s, s'), t). s) m) |∪| fimage (λ(uid, (s, s'), t). s') m"

lemma S_alt: "S t = EFSM.S (tm t)"
apply (simp add: S_def EFSM.S_def tm_def)
by force

lemma to_in_S:
"(∃to from uid. (uid, (from, to), t) |∈| xb ⟶ to |∈| S xb)"
by blast

lemma from_in_S:
"(∃to from uid. (uid, (from, to), t) |∈| xb ⟶ from |∈| S xb)"
by blast

subsection‹Building the PTA›
text‹The first step in EFSM inference is to construct a PTA from the observed traces in the same way
as for classical FSM inference. Beginning with the empty EFSM, we iteratively attempt to walk each
observed trace in the model. When we reach a point where there is no available transition, one is
added. For classical FSMs, this is simply an atomic label. EFSMs deal with data, so we need to add
guards which test for the observed input values and outputs which produce the observed values.›

primrec make_guard :: "value list ⇒ nat ⇒ vname gexp list" where
"make_guard [] _ = []" |
"make_guard (h#t) n = (gexp.Eq (V (vname.I n)) (L h))#(make_guard t (n+1))"

primrec make_outputs :: "value list ⇒ output_function list" where
"make_outputs [] = []" |
"make_outputs (h#t) = (L h)#(make_outputs t)"

definition max_uid_total :: "iEFSM ⇒ nat" where
"max_uid_total e = (case max_uid e of None ⇒ 0 | Some u ⇒ u)"

definition add_transition :: "iEFSM ⇒ cfstate ⇒ label ⇒ value list ⇒ value list ⇒ iEFSM" where
"add_transition e s label inputs outputs = finsert ([max_uid_total e + 1], (s, (maxS (tm e))+1), ⦇Label=label, Arity=length inputs, Guards=(make_guard inputs 0), Outputs=(make_outputs outputs), Updates=[]⦈) e"

fun make_branch :: "iEFSM ⇒ cfstate ⇒ registers ⇒ trace ⇒ iEFSM" where
"make_branch e _ _ [] = e" |
"make_branch e s r ((label, inputs, outputs)#t) =
(case (step (tm e) s r label inputs) of
Some (transition, s', outputs', updated) ⇒
if outputs' = (map Some outputs) then
make_branch e s' updated t
else
make_branch (add_transition e s label inputs outputs) ((maxS (tm e))+1) r t  |
None ⇒
make_branch (add_transition e s label inputs outputs) ((maxS (tm e))+1) r t
)"

primrec make_pta_aux :: "log ⇒ iEFSM ⇒ iEFSM" where
"make_pta_aux [] e = e" |
"make_pta_aux (h#t) e = make_pta_aux t (make_branch e 0 <> h)"

definition "make_pta log = make_pta_aux log {||}"

lemma make_pta_aux_fold [code]:
"make_pta_aux l e = fold (λh e. make_branch e 0 <> h) l e"
by(induct l arbitrary: e, auto)

subsection‹Integrating Heuristics›
text‹A key contribution of the inference technique presented in \<^cite>‹"foster2019"› is the ability to
introduce \emph{internal variables} to the model to generalise behaviours and allow transitions to
be merged. This is done by providing the inference technique with a set of \emph{heuristics}. The
aim here is not to create a one size fits all'' magic oracle, rather to recognise particular
\emph{data usage patterns} which can be abstracted.›

type_synonym update_modifier = "tids ⇒ tids ⇒ cfstate ⇒ iEFSM ⇒ iEFSM ⇒ iEFSM ⇒ (transition_matrix ⇒ bool) ⇒ iEFSM option"

definition null_modifier :: update_modifier where
"null_modifier f _ _ _ _ _ _ = None"

definition replace_transition :: "iEFSM ⇒ tids ⇒ transition ⇒ iEFSM" where
"replace_transition e uid new = (fimage (λ(uids, (from, to), t). if set uid ⊆ set uids then (uids, (from, to), new) else (uids, (from, to), t)) e)"

definition replace_all :: "iEFSM ⇒ tids list ⇒ transition ⇒ iEFSM" where
"replace_all e ids new = fold (λid acc. replace_transition acc id new) ids e"

definition replace_transitions :: "iEFSM ⇒ (tids × transition) list ⇒ iEFSM" where
"replace_transitions e ts = fold (λ(uid, new) acc. replace_transition acc uid new) ts e"

primrec try_heuristics_check :: "(transition_matrix ⇒ bool) ⇒ update_modifier list ⇒ update_modifier" where
"try_heuristics_check _ [] = null_modifier" |
"try_heuristics_check check (h#t) = (λa b c d e f ch.
case h a b c d e f ch of
Some e' ⇒ Some e' |
None ⇒ (try_heuristics_check check t) a b c d e f ch
)"

subsection‹Scoring State Merges›
text‹To tackle the state merging challenge, we need some means of determining which states are
compatible for merging. Because states are merged pairwise, we additionally require a way of
ordering the state merges. The potential merges are then sorted highest to lowest according to this
score such that we can merge states in order of their merge score.

We want to sort first by score (highest to lowest) and then by state pairs (lowest to highest) so we
endup merging the states with the highest scores first and then break ties by those state pairs
which are closest to the origin.›

record score =
Score :: nat
S1 :: cfstate
S2 :: cfstate

instantiation score_ext :: (linorder) linorder begin
definition less_score_ext :: "'a::linorder score_ext ⇒ 'a score_ext ⇒ bool" where
"less_score_ext t1 t2 = ((Score t2, S1 t1, S2 t1, more t1) < (Score t1, S1 t2, S2 t2, more t2) )"

definition less_eq_score_ext :: "'a::linorder score_ext ⇒ 'a::linorder score_ext ⇒ bool" where
"less_eq_score_ext s1 s2 = (s1 < s2 ∨ s1 = s2)"

instance
apply standard prefer 5
unfolding less_score_ext_def less_eq_score_ext_def
using score.equality apply fastforce
by auto
end

type_synonym scoreboard = "score fset"
type_synonym strategy = "tids ⇒ tids ⇒ iEFSM ⇒ nat"

definition outgoing_transitions :: "cfstate ⇒ iEFSM ⇒ (cfstate × transition × tids) fset" where
"outgoing_transitions s e = fimage (λ(uid, (from, to), t'). (to, t', uid)) ((ffilter (λ(uid, (origin, dest), t). origin = s)) e)"

primrec paths_of_length :: "nat ⇒ iEFSM ⇒ cfstate ⇒ tids list fset" where
"paths_of_length 0 _ _ = {|[]|}" |
"paths_of_length (Suc m) e s = (
let
outgoing = outgoing_transitions s e;
paths = ffUnion (fimage (λ(d, t, id). fimage (λp. id#p) (paths_of_length m e d)) outgoing)
in
ffilter (λl. length l = Suc m) paths
)"

lemma paths_of_length_1: "paths_of_length 1 e s = fimage (λ(d, t, id). [id]) (outgoing_transitions s e)"
apply (simp add: outgoing_transitions_def comp_def One_nat_def[symmetric])
apply (rule fBall_ffilter2)
defer
apply (simp add: ffilter_def ffUnion_def Abs_fset_inverse)
apply auto[1]
apply (simp add: ffilter_def ffUnion_def Abs_fset_inverse fset_both_sides)
by force

fun step_score :: "(tids × tids) list ⇒ iEFSM ⇒ strategy ⇒ nat" where
"step_score [] _ _ = 0" |
"step_score ((id1, id2)#t) e s = (
let score = s id1 id2 e in
if score = 0 then
0
else
score + (step_score t e s)
)"

lemma step_score_foldr [code]:
"step_score xs e s = foldr (λ(id1, id2) acc. let score = s id1 id2 e in
if score = 0 then
0
else
score + acc) xs 0"
proof(induct xs)
case Nil
then show ?case
by simp
next
case (Cons a xs)
then show ?case
apply (cases a, clarify)
qed

definition score_from_list :: "tids list fset ⇒ tids list fset ⇒ iEFSM ⇒ strategy ⇒ nat" where
"score_from_list P1 P2 e s = (
let
pairs = fimage (λ(l1, l2). zip l1 l2) (P1 |×| P2);
scored_pairs = fimage (λl. step_score l e s) pairs
in
fSum scored_pairs
)"

definition k_score :: "nat ⇒ iEFSM ⇒ strategy ⇒ scoreboard" where
"k_score k e strat = (
let
states = S e;
pairs_to_score = (ffilter (λ(x, y). x < y) (states |×| states));
paths = fimage (λ(s1, s2). (s1, s2, paths_of_length k e s1, paths_of_length k e s2)) pairs_to_score;
scores = fimage (λ(s1, s2, p1, p2). ⦇Score = score_from_list p1 p2 e strat, S1 = s1, S2 = s2⦈) paths
in
ffilter (λx. Score x > 0) scores
)"

definition score_state_pair :: "strategy ⇒ iEFSM ⇒ cfstate ⇒ cfstate ⇒ nat" where
"score_state_pair strat e s1 s2 = (
let
T1 = outgoing_transitions s1 e;
T2 = outgoing_transitions s2 e
in
fSum (fimage (λ((_, _, t1), (_, _, t2)). strat t1 t2 e) (T1 |×| T2))
)"

definition score_1 :: "iEFSM ⇒ strategy ⇒ scoreboard" where
"score_1 e strat = (
let
states = S e;
pairs_to_score = (ffilter (λ(x, y). x < y) (states |×| states));
scores = fimage (λ(s1, s2). ⦇Score = score_state_pair strat e s1 s2, S1 = s1, S2 = s2⦈) pairs_to_score
in
ffilter (λx. Score x > 0) scores
)"

lemma score_1: "score_1 e s = k_score 1 e s"
proof-
have fprod_fimage:
"⋀a b. ((λ(_, _, id). [id]) || a |×| (λ(_, _, id). [id]) || b) =
fimage (λ((_, _, id1), (_, _, id2)). ([id1], [id2])) (a |×| b)"
apply (simp add: fimage_def fprod_def Abs_fset_inverse fset_both_sides)
by force
show ?thesis
apply (simp add: score_1_def k_score_def Let_def comp_def)
apply (rule arg_cong[of _ _ "ffilter (λx. 0 < Score x)"])
apply (rule fun_cong[of _ _ "(Inference.S e |×| Inference.S e)"])
apply (rule ext)
subgoal for x
apply (rule fun_cong[of _ _ "ffilter (λa. case a of (a, b) ⇒ a < b) x"])
apply (rule arg_cong[of _ _ fimage])
apply (rule ext)
subgoal for x
apply (case_tac x)
apply simp
apply (simp add: score_state_pair_def Let_def score_from_list_def comp_def)
subgoal for a b
apply (rule arg_cong[of _ _ fSum])
apply (rule fun_cong[of _ _ "(outgoing_transitions a e |×| outgoing_transitions b e)"])
apply (rule arg_cong[of _ _ fimage])
apply (rule ext)
apply clarify
done
done
done
qed

fun bool2nat :: "bool ⇒ nat" where
"bool2nat True = 1" |
"bool2nat False = 0"

definition score_transitions :: "transition ⇒ transition ⇒ nat" where
"score_transitions t1 t2 = (
if Label t1 = Label t2 ∧ Arity t1 = Arity t2 ∧ length (Outputs t1) = length (Outputs t2) then
1 + bool2nat (t1 = t2) + card ((set (Guards t2)) ∩ (set (Guards t2))) + card ((set (Updates t2)) ∩ (set (Updates t2))) + card ((set (Outputs t2)) ∩ (set (Outputs t2)))
else
0
)"

subsection‹Merging States›
definition merge_states_aux :: "nat ⇒ nat ⇒ iEFSM ⇒ iEFSM" where
"merge_states_aux s1 s2 e = fimage (λ(uid, (origin, dest), t). (uid, (if origin = s1 then s2 else origin , if dest = s1 then s2 else dest), t)) e"

definition merge_states :: "nat ⇒ nat ⇒ iEFSM ⇒ iEFSM" where
"merge_states x y t = (if x > y then merge_states_aux x y t else merge_states_aux y x t)"

lemma merge_states_symmetry: "merge_states x y t = merge_states y x t"

lemma merge_state_self: "merge_states s s t = t"
by force

lemma merge_states_self_simp [code]:
"merge_states x y t = (if x = y then t else if x > y then merge_states_aux x y t else merge_states_aux y x t)"
by force

subsection‹Resolving Nondeterminism›
text‹Because EFSM transitions are not simply atomic actions, duplicated behaviours cannot be
resolved into a single transition by simply merging destination states, as it can in classical FSM
inference. It is now possible for attempts to resolve the nondeterminism introduced by merging
states to fail, meaning that two states which initially seemed compatible cannot actually be merged.
This is not the case in classical FSM inference.›

type_synonym nondeterministic_pair = "(cfstate × (cfstate × cfstate) × ((transition × tids) × (transition × tids)))"

definition state_nondeterminism :: "nat ⇒ (cfstate × transition × tids) fset ⇒ nondeterministic_pair fset" where
"state_nondeterminism og nt = (if size nt < 2 then {||} else ffUnion (fimage (λx. let (dest, t) = x in fimage (λy. let (dest', t') = y in (og, (dest, dest'), (t, t'))) (nt - {|x|})) nt))"

lemma state_nondeterminism_empty [simp]: "state_nondeterminism a {||} = {||}"
by (simp add: state_nondeterminism_def ffilter_def Set.filter_def)

lemma state_nondeterminism_singledestn [simp]: "state_nondeterminism a {|x|} = {||}"
by (simp add: state_nondeterminism_def ffilter_def Set.filter_def)

(* For each state, get its outgoing transitions and see if there's any nondeterminism there *)
definition nondeterministic_pairs :: "iEFSM ⇒ nondeterministic_pair fset" where
"nondeterministic_pairs t = ffilter (λ(_, _, (t, _), (t', _)). Label t = Label t' ∧ Arity t = Arity t' ∧ choice t t') (ffUnion (fimage (λs. state_nondeterminism s (outgoing_transitions s t)) (S t)))"

definition nondeterministic_pairs_labar_dest :: "iEFSM ⇒ nondeterministic_pair fset" where
"nondeterministic_pairs_labar_dest t = ffilter
(λ(_, (d, d'), (t, _), (t', _)).
Label t = Label t' ∧ Arity t = Arity t' ∧ (choice t t' ∨ (Outputs t = Outputs t' ∧ d = d')))
(ffUnion (fimage (λs. state_nondeterminism s (outgoing_transitions s t)) (S t)))"

definition nondeterministic_pairs_labar :: "iEFSM ⇒ nondeterministic_pair fset" where
"nondeterministic_pairs_labar t = ffilter
(λ(_, (d, d'), (t, _), (t', _)).
Label t = Label t' ∧ Arity t = Arity t' ∧ (choice t t' ∨ Outputs t = Outputs t'))
(ffUnion (fimage (λs. state_nondeterminism s (outgoing_transitions s t)) (S t)))"

definition deterministic :: "iEFSM ⇒ (iEFSM ⇒ nondeterministic_pair fset) ⇒ bool" where
"deterministic t np = (np t = {||})"

definition nondeterministic :: "iEFSM ⇒ (iEFSM ⇒ nondeterministic_pair fset) ⇒ bool" where
"nondeterministic t np = (¬ deterministic t np)"

definition insert_transition :: "tids ⇒ cfstate ⇒ cfstate ⇒ transition ⇒ iEFSM ⇒ iEFSM" where
"insert_transition uid from to t e = (
if ∄(uid, (from', to'), t') |∈| e. from = from' ∧ to = to' ∧ t = t' then
finsert (uid, (from, to), t) e
else
fimage (λ(uid', (from', to'), t').
if from = from' ∧ to = to' ∧ t = t' then
(List.union uid' uid, (from', to'), t')
else
(uid', (from', to'), t')
) e
)"

definition make_distinct :: "iEFSM ⇒ iEFSM" where
"make_distinct e = ffold_ord (λ(uid, (from, to), t) acc. insert_transition uid from to t acc) e {||}"

― ‹When we replace one transition with another, we need to merge their uids to keep track of which›
― ‹transition accounts for which action in the original traces                                     ›
definition merge_transitions_aux :: "iEFSM ⇒ tids ⇒ tids ⇒ iEFSM" where
"merge_transitions_aux e oldID newID = (let
(uids1, (origin, dest), old) = fthe_elem (ffilter (λ(uids, _). oldID = uids) e);
(uids2, (origin, dest), new) = fthe_elem (ffilter (λ(uids, _). newID = uids) e) in
make_distinct (finsert (List.union uids1 uids2, (origin, dest), new) (e - {|(uids1, (origin, dest), old), (uids2, (origin, dest), new)|}))
)"

(* merge_transitions - Try dest merge transitions t1 and t2 dest help resolve nondeterminism in
newEFSM. If either subsumes the other directly then the subsumed transition
can simply be replaced with the subsuming one, else we try dest apply the
modifier function dest resolve nondeterminism that way.                    *)
(* @param oldEFSM   - the EFSM before merging the states which caused the nondeterminism          *)
(* @param preDestMerge   - the EFSM after merging the states which caused the nondeterminism      *)
(* @param newEFSM   - the current EFSM with nondeterminism                                        *)
(* @param t1        - a transition dest be merged with t2                                         *)
(* @param u1        - the unique identifier of t1                                                 *)
(* @param t2        - a transition dest be merged with t1                                         *)
(* @param u2        - the unique identifier of t2                                                 *)
(* @param modifier  - an update modifier function which tries dest generalise transitions         *)
definition merge_transitions :: "(cfstate × cfstate) set ⇒ iEFSM ⇒ iEFSM ⇒ iEFSM ⇒ transition ⇒ tids ⇒ transition ⇒ tids ⇒ update_modifier ⇒ (transition_matrix ⇒ bool) ⇒ iEFSM option" where
"merge_transitions failedMerges oldEFSM preDestMerge destMerge t1 u1 t2 u2 modifier check = (
if ∀id ∈ set u1. directly_subsumes (tm oldEFSM) (tm destMerge) (origin [id] oldEFSM) (origin u1 destMerge) t2 t1 then
― ‹Replace t1 with t2›
Some (merge_transitions_aux destMerge u1 u2)
else if ∀id ∈ set u2. directly_subsumes (tm oldEFSM) (tm destMerge) (origin [id] oldEFSM) (origin u2 destMerge) t1 t2 then
― ‹Replace t2 with t1›
Some (merge_transitions_aux destMerge u2 u1)
else
case modifier u1 u2 (origin u1 destMerge) destMerge preDestMerge oldEFSM check of
None ⇒ None |
Some e ⇒ Some (make_distinct e)
)"

definition outgoing_transitions_from :: "iEFSM ⇒ cfstate ⇒ transition fset" where
"outgoing_transitions_from e s = fimage (λ(_, _, t). t) (ffilter (λ(_, (orig, _), _). orig = s) e)"

definition order_nondeterministic_pairs :: "nondeterministic_pair fset ⇒ nondeterministic_pair list" where
"order_nondeterministic_pairs s = map snd (sorted_list_of_fset (fimage (λs. let (_, _, (t1, _), (t2, _)) = s in (score_transitions t1 t2, s)) s))"

(* resolve_nondeterminism - tries dest resolve nondeterminism in a given iEFSM                      *)
(* @param ((from, (dest1, dest2), ((t1, u1), (t2, u2)))#ss) - a list of nondeterministic pairs where
from - nat - the state from which t1 and t2 eminate
dest1  - nat - the destination state of t1
dest2  - nat - the destination state of t2
t1   - transition - a transition dest be merged with t2
t2   - transition - a transition dest be merged with t1
u1   - nat - the unique identifier of t1
u2   - nat - the unique identifier of t2
ss   - list - the rest of the list                                                      *)
(* @param oldEFSM - the EFSM before merging the states which caused the nondeterminism            *)
(* @param newEFSM - the current EFSM with nondeterminism                                          *)
(* @param m       - an update modifier function which tries dest generalise transitions             *)
(* @param check - a function which takes an EFSM and returns a bool dest ensure that certain
properties hold in the new iEFSM                                                *)
function resolve_nondeterminism :: "(cfstate × cfstate) set ⇒ nondeterministic_pair list ⇒ iEFSM ⇒ iEFSM ⇒ update_modifier ⇒ (transition_matrix ⇒ bool) ⇒ (iEFSM ⇒ nondeterministic_pair fset) ⇒ (iEFSM option × (cfstate × cfstate) set)" where
"resolve_nondeterminism failedMerges [] _ newEFSM _ check np = (
if deterministic newEFSM np ∧ check (tm newEFSM) then Some newEFSM else None, failedMerges
)" |
"resolve_nondeterminism failedMerges ((from, (dest1, dest2), ((t1, u1), (t2, u2)))#ss) oldEFSM newEFSM m check np = (
if (dest1, dest2) ∈ failedMerges ∨ (dest2, dest1) ∈ failedMerges then
(None, failedMerges)
else
let destMerge = merge_states dest1 dest2 newEFSM in
case merge_transitions failedMerges oldEFSM newEFSM destMerge t1 u1 t2 u2 m check of
None ⇒ resolve_nondeterminism (insert (dest1, dest2) failedMerges) ss oldEFSM newEFSM m check np |
Some new ⇒ (
let newScores = order_nondeterministic_pairs (np new) in
if (size new, size (S new), size (newScores)) < (size newEFSM, size (S newEFSM), size ss) then
case resolve_nondeterminism failedMerges newScores oldEFSM new m check np of
(Some new', failedMerges) ⇒ (Some new', failedMerges) |
(None, failedMerges) ⇒ resolve_nondeterminism (insert (dest1, dest2) failedMerges) ss oldEFSM newEFSM m check np
else
(None, failedMerges)
)
)"
apply (clarify, metis neq_Nil_conv prod_cases3 surj_pair)
by auto
termination
by (relation "measures [λ(_, _, _, newEFSM, _). size newEFSM,
λ(_, _, _, newEFSM, _). size (S newEFSM),
λ(_, ss, _, _, _). size ss]", auto)

subsection‹EFSM Inference›

(* Merge - tries dest merge two states in a given iEFSM and resolve the resulting nondeterminism  *)
(* @param e     - an iEFSM                                                                        *)
(* @param s1    - a state dest be merged with s2                                                  *)
(* @param s2    - a state dest be merged with s1                                                  *)
(* @param m     - an update modifier function which tries dest generalise transitions             *)
(* @param check - a function which takes an EFSM and returns a bool dest ensure that certain
properties hold in the new iEFSM                                                *)
definition merge :: "(cfstate × cfstate) set ⇒ iEFSM ⇒ nat ⇒ nat ⇒ update_modifier ⇒ (transition_matrix ⇒ bool) ⇒ (iEFSM ⇒ nondeterministic_pair fset) ⇒ (iEFSM option × (cfstate × cfstate) set)" where
"merge failedMerges e s1 s2 m check np = (
if s1 = s2 ∨ (s1, s2) ∈ failedMerges ∨ (s2, s1) ∈ failedMerges then
(None, failedMerges)
else
let e' = make_distinct (merge_states s1 s2 e) in
resolve_nondeterminism failedMerges (order_nondeterministic_pairs (np e')) e e' m check np
)"

(* inference_step - attempt dest carry out a single step of the inference process by merging the  *)
(* @param e - an iEFSM dest be generalised                                                        *)
(* @param ((s, s1, s2)#t) - a list of triples of the form (score, state, state) dest be merged    *)
(* @param m     - an update modifier function which tries dest generalise transitions             *)
(* @param check - a function which takes an EFSM and returns a bool dest ensure that certain
properties hold in the new iEFSM                                                *)
function inference_step :: "(cfstate × cfstate) set ⇒ iEFSM ⇒ score fset ⇒ update_modifier ⇒ (transition_matrix ⇒ bool) ⇒ (iEFSM ⇒ nondeterministic_pair fset) ⇒ (iEFSM option × (cfstate × cfstate) set)" where
"inference_step failedMerges e s m check np = (
if s = {||} then (None, failedMerges) else
let
h = fMin s;
t = s - {|h|}
in
case merge failedMerges e (S1 h) (S2 h) m check np of
(Some new, failedMerges) ⇒ (Some new, failedMerges) |
(None, failedMerges) ⇒ inference_step (insert ((S1 h), (S2 h)) failedMerges) e t m check np
)"
by auto
termination
by (relation "measures [λ(_, _, s, _, _, _). size s]") (auto dest!: card_minus_fMin)

(* Takes an iEFSM and iterates inference_step until no further states can be successfully merged  *)
(* @param e - an iEFSM dest be generalised                                                        *)
(* @param r - a strategy dest identify and prioritise pairs of states dest merge                  *)
(* @param m     - an update modifier function which tries dest generalise transitions             *)
(* @param check - a function which takes an EFSM and returns a bool dest ensure that certain
properties hold in the new iEFSM                                                *)
function infer :: "(cfstate × cfstate) set ⇒ nat ⇒ iEFSM ⇒ strategy ⇒ update_modifier ⇒ (transition_matrix ⇒ bool) ⇒ (iEFSM ⇒ nondeterministic_pair fset) ⇒ iEFSM" where
"infer failedMerges k e r m check np = (
let scores = if k = 1 then score_1 e r else (k_score k e r) in
case inference_step failedMerges e (ffilter (λs. (S1 s, S2 s) ∉ failedMerges ∧ (S2 s, S1 s) ∉ failedMerges) scores) m check np of
(None, _) ⇒ e |
(Some new, failedMerges) ⇒ if (S new) |⊂| (S e) then infer failedMerges k new r m check np else e
)"
by auto
termination
apply (relation "measures [λ(_, _, e, _). size (S e)]")
apply simp
by (metis (no_types, lifting) case_prod_conv measures_less size_fsubset)

fun get_ints :: "trace ⇒ int list" where
"get_ints [] = []" |
"get_ints ((_, inputs, outputs)#t) = (map (λx. case x of Num n ⇒ n) (filter is_Num (inputs@outputs)))"

definition learn :: "nat ⇒ iEFSM ⇒ log ⇒ strategy ⇒ update_modifier ⇒ (iEFSM ⇒ nondeterministic_pair fset) ⇒ iEFSM" where
"learn n pta l r m np = (
let check = accepts_log (set l) in
(infer {} n pta r m check np)
)"

subsection‹Evaluating Inferred Models›
text‹We need a function to test the EFSMs we infer. The \texttt{test\_trace} function executes a
trace in the model and outputs a more comprehensive trace such that the expected outputs and actual
outputs can be compared. If a point is reached where the model does not recognise an action, the
remainder of the trace forms the second element of the output pair such that we know the exact point
at which the model stopped processing.›

definition i_possible_steps :: "iEFSM ⇒ cfstate ⇒ registers ⇒ label ⇒ inputs ⇒ (tids × cfstate × transition) fset" where
"i_possible_steps e s r l i = fimage (λ(uid, (origin, dest), t). (uid, dest, t))
(ffilter (λ(uid, (origin, dest::nat), t::transition).
origin = s
∧ (Label t) = l
∧ (length i) = (Arity t)
∧ apply_guards (Guards t) (join_ir i r)
)
e)"

fun test_trace :: "trace ⇒ iEFSM ⇒ cfstate ⇒ registers ⇒ ((label × inputs × cfstate × cfstate × registers × tids × value list × outputs) list × trace)" where
"test_trace [] _ _ _ = ([], [])" |
"test_trace ((l, i, expected)#es) e s r = (
let
ps = i_possible_steps e s r l i
in
if fis_singleton ps then
let
(id, s', t) = fthe_elem ps;
r' = evaluate_updates t i r;
actual = evaluate_outputs t i r;
(est, fail) = (test_trace es e s' r')
in
((l, i, s, s', r, id, expected, actual)#est, fail)
else
([], (l, i, expected)#es)
)"

text‹The \texttt{test\_log} function executes the \texttt{test\_trace} function on a collection of
traces known as the \emph{test set.}›
definition test_log :: "log ⇒ iEFSM ⇒ ((label × inputs × cfstate × cfstate × registers × tids × value list × outputs) list × trace) list" where
"test_log l e = map (λt. test_trace t e 0 <>) l"

end