diff --git a/logic/service.go b/logic/service.go
new file mode 100644
index 0000000..ba6c3cd
--- /dev/null
+++ b/logic/service.go
@@ -0,0 +1,21 @@
+package logic
+
+import "git.dragon-labs.de/alphyron/group_helper/models"
+
+type GroupHelperService interface {
+	CreateGroup(*models.Group) (*models.Group, error)
+	UpdateGroup(*models.Group) (*models.Group, error)
+
+	GetGroupByID(int64) (*models.Group, error)
+	GetGroupDatabaseSize(int64) (int, error)
+
+	CreateUser(*models.User) (*models.User, error)
+	GetUserByID(int64) *models.User
+
+	UserJoinGroup(*models.User, *models.Group) (bool, error)
+	UserLeaveGroup(*models.User, *models.Group) (bool, error)
+	IsUserInGroup(*models.User, *models.Group) (bool, error)
+
+	ListGroups() ([]*models.Group, error)
+	ListUsers() ([]*models.User, error)
+}
diff --git a/models/group.go b/models/group.go
new file mode 100644
index 0000000..09ad143
--- /dev/null
+++ b/models/group.go
@@ -0,0 +1,35 @@
+package models
+
+type Group struct {
+	ID                  uint `gorm:"primary_key"`
+	GroupID             int64
+	Size                int
+	UserJoinMessage     string `gorm:"column:msg_user_join;type:text"`
+	UserVerifiedMessage string `gorm:"column:msg_user_verified;type:text"`
+	UserLeaveMessage    string `gorm:"column:msg_user_leave;type:text"`
+	UserKickMessage     string `gorm:"column:msg_user_kick;type:text"`
+	ForbidWriting       bool   `gorm:"column:forbid_writing"`
+	OnlineCheck         int    `gorm:"column:kick_cooldown"`
+}
+
+func (group *Group) FillDefaultValues() {
+	if len(group.UserKickMessage) == 0 {
+		group.UserKickMessage = "[{{user.firstname}} {{user.lastname}}](tg://user?id={{user.id}}) did not verify!\n They are going to leave us."
+	}
+
+	if len(group.UserJoinMessage) == 0 {
+		group.UserJoinMessage = "[{{user.firstname}} {{user.lastname}}](tg://user?id={{user.id}}) joined us. Hello and Welcome! Please verify that you are not a bot."
+	}
+
+	if len(group.UserLeaveMessage) == 0 {
+		group.UserLeaveMessage = "[{{user.firstname}} {{user.lastname}}](tg://user?id={{user.id}}) left us."
+	}
+
+	if len(group.UserVerifiedMessage) == 0 {
+		group.UserVerifiedMessage = "[{{user.firstname}} {{user.lastname}}](tg://user?id={{user.id}}) is now permitted to stay in the chat!"
+	}
+
+	if group.OnlineCheck == 0 {
+		group.OnlineCheck = 5
+	}
+}
diff --git a/models/user.go b/models/user.go
new file mode 100644
index 0000000..d517522
--- /dev/null
+++ b/models/user.go
@@ -0,0 +1,7 @@
+package models
+
+type User struct {
+	ID     uint     `gorm:"primary_key" json:"id"`
+	UserID int64    `json:"user_id"`
+	Groups []*Group `json:"groups" gorm:"many2many:GroupUser;"`
+}