diff --git a/README.md b/README.md
index c5a7682..b741908 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,2 @@
-Use ```bash
-uv build
-```
+Use ``uv build``
 to build package. Then git commit & push. 
\ No newline at end of file
diff --git a/pyproject.toml b/pyproject.toml
index 98983b5..223c779 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -10,7 +10,7 @@ dependencies = [
 ]
 
 [build-system]
-requires = ["uv_build>=0.10.2,<0.11.0"]
+requires = ["uv_build>=0.10.2,<0.12"]
 build-backend = "uv_build"
 
 [dependency-groups]
diff --git a/src/fiber_package/entities/member.py b/src/fiber_package/entities/member.py
index d30dba3..3499199 100644
--- a/src/fiber_package/entities/member.py
+++ b/src/fiber_package/entities/member.py
@@ -1,4 +1,4 @@
-from typing import Annotated
+from typing import Literal
 from pydantic import Field
 
 from .non_members import FormerMemberModel
@@ -6,7 +6,8 @@ from .enums import Membership, OnlineAlmanacField
 from .submodels import Address, LoginInfo
 
 class MemberModel(FormerMemberModel):
-    membership: Annotated[Membership, Field(pattern="member")]
+    # requires that Membership equals member
+    membership: Literal[Membership.member] = Membership.member
 
     login: LoginInfo
     address: Address
diff --git a/src/fiber_package/entities/non_members.py b/src/fiber_package/entities/non_members.py
index afc29bb..7eb3856 100644
--- a/src/fiber_package/entities/non_members.py
+++ b/src/fiber_package/entities/non_members.py
@@ -1,4 +1,4 @@
-from typing import Annotated
+from typing import Literal
 from pydantic import Field
 
 from .person import PersonModel
@@ -13,12 +13,12 @@ class FormerMemberModel(PersonModel):
     # company emails?
 
 class AlumnModel(FormerMemberModel):
-    membership: Annotated[Membership, Field(pattern="alumn")]
+    membership: Literal[Membership.alumn] = Membership.alumn
 
     graduated: bool = False
     receive_spam_mail: bool = True
 
 class ExternalModel(PersonModel):
-    membership: Annotated[Membership, Field(pattern="extern")]
+    membership: Literal[Membership.extern] = Membership.extern
     # TODO... payment???
     # TODO require login info??
diff --git a/src/fiber_package/groups/association.py b/src/fiber_package/groups/association.py
index 6a1011a..d5fcea7 100644
--- a/src/fiber_package/groups/association.py
+++ b/src/fiber_package/groups/association.py
@@ -1,12 +1,12 @@
 from pydantic import BaseModel
 
-from fiber_package.util import EntityList
+from fiber_package.util import EntityList, GroupList
 
 class AssociationModel(BaseModel):
     full_name: str
-    members: EntityList = EntityList("member", [])
-    # committees: GroupList("commmittee", 0) # type: ignore
-    # events: GroupList("event", 0) # type: ignore
-    # activities: GroupList("activity", 0) # type: ignore
-    # mailings: GroupList("mailing", 0) # type: ignore
-    # mailalias: GroupList("mailalias", 0) # type: ignore
\ No newline at end of file
+    members: EntityList
+    committees: GroupList
+    guilds: GroupList
+    # events: GroupList
+    # activities: GroupList
+    # mailings: GroupList
\ No newline at end of file
diff --git a/src/fiber_package/groups/committees/committee.py b/src/fiber_package/groups/committees/committee.py
new file mode 100644
index 0000000..ff071f8
--- /dev/null
+++ b/src/fiber_package/groups/committees/committee.py
@@ -0,0 +1,50 @@
+from pydantic import BaseModel, model_validator
+from fiber_package.util import EntityList, GroupList, GroupRef
+
+from typing import Self
+from datetime import date
+
+from .enums import CommitteeType
+
+'''
+Committees are groups of members for a definite period.
+Every committee has a list of editions.
+An edition is a definite group of members with functions and a timespan.
+'''
+
+class CommitteeModel(BaseModel):
+    full_name_EN: str
+    full_name_NL: str
+    description_EN: str = ""
+    description_NL: str = ""
+    committee_type: CommitteeType
+
+    active: bool = True
+
+    editions: GroupList
+    current_edition: GroupRef | None
+
+    @model_validator(mode='after')
+    def current_edition_in_editions(self) -> Self:
+        uuid = self.current_edition
+        if uuid is None:
+            return self
+        if uuid not in self.editions:
+            raise ValueError("Current edition must be in list of editions")
+        return self
+
+    # TODO... maybe require that an active board always has a current_edition that is non-empty?
+
+class CommitteeEditionModel(BaseModel):
+    members: EntityList
+    functions: dict[UUID4, str]
+
+    start_date: date
+    end_date: date | None # None means ongoing
+
+    @model_validator(mode='after')
+    def functions_to_members_only(self) -> Self:
+        for uuid in self.functions.keys():
+            if uuid not in self.members:
+                raise ValueError("Cannot only assign functions to members")
+        return self
\ No newline at end of file
diff --git a/src/fiber_package/groups/committees/enums.py b/src/fiber_package/groups/committees/enums.py
new file mode 100644
index 0000000..0c1234d
--- /dev/null
+++ b/src/fiber_package/groups/committees/enums.py
@@ -0,0 +1,8 @@
+from enum import StrEnum
+
+class CommitteeType(StrEnum):
+    board_committee = "Board committee"
+    gmm_committee = "GMM committee"
+    board = "board"
+
+
diff --git a/src/fiber_package/groups/committees/guild.py b/src/fiber_package/groups/committees/guild.py
new file mode 100644
index 0000000..e21e107
--- /dev/null
+++ b/src/fiber_package/groups/committees/guild.py
@@ -0,0 +1,42 @@
+from pydantic import BaseModel, model_validator
+from fiber_package.util import EntityList
+
+from datetime import date
+
+from typing import Self
+
+
+'''
+Guilds are groups of members for an indefinite period.
+They have a list of members.
+
+Removing old members from last_active is done in fiber
+'''
+
+class GuildModel(BaseModel):
+    full_name_EN: str
+    full_name_NL: str
+    description_EN: str
+    description_NL: str
+
+    members: EntityList
+    previous_members: EntityList
+
+    guild_masters: EntityList
+
+    last_active: dict[EntityRef, date]
+
+    @model_validator(mode='after')
+    def current_members_not_previous(self) -> Self:
+        for member in self.members:
+            if member in self.previous_members:
+                raise ValueError("There can be no overlap between members and previous members!")
+        return self
+
+    @model_validator(mode='after')
+    def guild_masters_are_members(self) -> Self:
+        for master in self.guild_masters:
+            if master not in self.members:
+                raise ValueError("All guild masters must be members!")
+        return self
+        
\ No newline at end of file
diff --git a/src/fiber_package/groups/root.py b/src/fiber_package/groups/root.py
index 594962e..2d3bfbd 100644
--- a/src/fiber_package/groups/root.py
+++ b/src/fiber_package/groups/root.py
@@ -2,5 +2,5 @@ from pydantic import BaseModel
 from fiber_package.util import GroupList, EntityList
 
 class RootGroupModel(BaseModel):
-    associations: GroupList = GroupList("association", [])
-    sys_admins: EntityList = EntityList("login", [])
\ No newline at end of file
+    associations: GroupList
+    sys_admins: EntityList
\ No newline at end of file
diff --git a/src/fiber_package/util.py b/src/fiber_package/util.py
index 6077523..76dbc08 100644
--- a/src/fiber_package/util.py
+++ b/src/fiber_package/util.py
@@ -1,23 +1,9 @@
-from dataclasses import dataclass, field
+from typing import Annotated
+from pydantic import RootModel, Field, UUID4
 
-from pydantic import UUID4
 
-@dataclass(slots=True)
-class EntityList:
-    template: str
-    uuids: list[UUID4] = field(default_factory=list)
+EntityList = Annotated[list[UUID4], Field(default_factory=list)]
+GroupList  = Annotated[list[UUID4], Field(default_factory=list)]
 
-@dataclass(slots=True)
-class GroupList:
-    template: str
-    uuids: list[UUID4] = field(default_factory=list)
-
-@dataclass(slots=True)
-class EntityRef:
-    template: str
-    uuid: UUID4 | None = None
-
-@dataclass(slots=True)
-class GroupRef:
-    template: str
-    uuid: UUID4 | None = None
+EntityRef = UUID4
+GroupRef = UUID4