1.1. Ontology in the Halal Industries

Nowadays, ontology has gained attention in the halal industry. According to Omar et al. (2013), the halal industry has experienced the most rapid global growth within the business landscape of Malaysia. Nevertheless, the issuance of the halal certificate is a time-consuming process (Muhammad et al., 2020). According to an interview with halal management auditors, the auditors encountered difficulties detecting the halal status of ingredients, notably flavourings, because most flavourings do not have halal certificates in the application of halal certification of food products. Thus, the absence of halal certificates required the halal management auditors to trace the halal status of the ingredients in order to process the application of the halal status. One significant limitation is the lack of uniformity in the terminology employed by food manufacturers and halal management auditors. This inconsistency poses challenges for halal management auditors in effectively verifying the halal status of ingredients, particularly in cases involving flavourings (Hashim et al., 2017).

1.2. Issues of Flavourings

In order to decide the halal status of flavourings, the halal management auditors need to identify the raw materials used together with their sources, whether they are derived from animals, plants, or chemicals (Ali et al., 2017). Determining the source of raw materials is crucial in the traceability of halal status (Ali et al., 2017; Hashim et al., 2017). Technical and sharia aspects are required to determine the halal status of raw materials for flavouring (Hashim et al., 2016; Omar & Jaafar, 2011; Shafii & Siti Khadijah, 2012). The technical components include ingredient specifications, production process charts, life storage duration, laboratory result analysis, allergy information, and storage methods. From a sharia perspective, it is imperative to adhere to certain restrictions pertaining to the cleanliness of materials, abstinence from alcohol, absence of blood, absence of pork, and ensuring their harmlessness. However, both technical and sharia aspects require the knowledge of experts to decide on the halal status of flavourings (Hashim et al., 2017). Various sources of information are required to suggest the halal status of flavourings, such as the Handbook of Fenaroli, Chemical Entities of Biological Interest (ChEBI), and academic journals related to flavouring. According to the halal management auditors, they have to refer to the sources separately as the sources are not aggregated in a single repository. Thus, there is no integration of the sources for halal auditors to refer to in order to determine the halal status of flavourings.

1.3. Problem Statement and Scope of Research

Due to the variety of sources used to determine the halal status of flavourings, which may cause conceptual inconsistencies between the terms used in the resources, ontology is one of the practical ways to solve the issue. This phenomenon is also evident in a previous study undertaken by Omar et al. (2013) regarding the development of a system for verifying the halal status of ingredients, which engaged in constructing an E-Numbers ontology by integrating data from multiple databases. Their research sought to assist the Muslim community in confirming the halal status of products in the market with E-Numbers. The integration of several E-Numbers databases was facilitated through the utilisation of ontology. This approach was motivated by Jagadish (1990)’s assertion that ontologies play a crucial role in integrating heterogeneous databases while providing a consistent vocabulary. The rationales behind the variety of reference sources used in developing a flavouring ontology are as follows:

As a result, in this research, the ontology provides a standardised and formal representation of knowledge, allowing for the harmonisation and integration of diverse flavouring databases. By establishing a common vocabulary and a shared understanding of the relationships between different terms, ontology facilitates accurate and consistent determination of the halal status of flavourings. It enables halal management auditors to effectively analyse and interpret information from multiple sources, reducing the complexity and subjectivity involved in assessing the halal compliance of flavourings. Ultimately, an ontology-based approach empowers the halal management auditors to make informed decisions and streamline the process of determining the halal status of flavourings, thus enhancing the efficiency and reliability of the halal certification process for food producers. The research aims to answer the following research questions:

This paper aims to describe the process of developing a flavouring ontology by adapting the steps suggested by Noy and McGuinness (2001). The paper is organised as follows: Section 2 discusses the flavouring domain, Section 3 discusses the methods involved in developing the flavouring ontology, and Section 4 discusses the implementation of the ontology with Protégé and the evaluation of the flavouring ontology. Finally, Sections 5 and 6, respectively, present the discussion and the conclusions of this work.

3.1. Specification: Ontology Goal and Scope

The definition of ontology goal and scope is the first step of the specification phase, as illustrated in the 101 Method (Noy & McGuinness, 2001). The scope of the ontology determines the specific inclusions and exclusions. It is crucial to reduce the amount of data and concepts that need to be analysed for a certain field, particularly considering the intricacy of the semantic nuances. This ontology mainly focuses on determining the halal status of flavouring and the synonym of the flavouring term.

Enumerating the competency questions is a method for establishing the scope of the ontology. It can be accomplished by formulating a series of inquiries that an ontology-based knowledge base should possess the capability to provide answers for. Table 1 presents the competency questions pertaining to the topic of flavouring. The ontology must possess the capability to address these informal inquiries, which aim to evaluate the alignment between the ontology and its intended objectives.

These competency questions are some of the required information that halal auditors need to know in order for them to check the halal status of flavourings that do not have their own halal certification. These competency questions also guide the researcher in developing the ontology within the scope. For the information on flavouring, there are some metadata elements that the halal auditors need to know, such as halal status, synonyms, type of raw material, botanical name, synthesis, and natural occurrence.

3.2. Specification: Domain Description

We begin with the domain analysis task, where the halal certification manual was studied and revised. We gathered information regarding the process of processing the application for halal certificates. Besides this, we also explored whether there are existing ontologies that serve as a reference for constructing our initial ontology. Through our efforts, we utilised the analytical task to convert listed terms into the conceptualised structure for the flavouring ontology. Drawing from the existing ontology with diverse listed terms served as a blueprint to steer the development of our inaugural ontology. In addition, we met with experts who are the auditors from Jabatan Kemajuan Islam Malaysia (JAKIM)’s Halal Management Division to corroborate the veracity of the issues raised. The halal management auditors were chosen because they were experts in the halal certification processing field. The halal management auditors and researchers who bring information to support these tasks have assimilated the issues. For instance, during the interview, the halal management auditors confirmed that flavouring information, such as types of raw materials and halal status, is an important element in the flavouring domain. At the same time, the researchers brought technical knowledge support, such as ontology mapping, to this task. Ontology mapping is a process of integrating information from various sources (Kazani et al., 2023). There are several sources involved in developing the flavouring ontology, as showsn in Table 2 (Jabatan Kemajuan Islam Malaysia, 2015).

Ultimately, we established the intermediate representations utilised for knowledge acquisition, with Table 3 displaying fundamental terms within the flavouring domain.

From Table 3, the basic terms of the flavouring domain are the important metadata required for halal auditors to trace the halal status of flavourings. These basic terms of the flavouring domain were manually extracted and defined through brainstorming sessions with domain experts and also by referring to the flavouring handbook, which is the Handbook of Fenaroli.

3.3. Conceptualisation: Define the Classes and the Class Hierarchy

The class hierarchy for ontology can be developed in three possible ways: top-down, bottom-up, or a combination of both (Noy & McGuinness, 2001). We chose the combination of both as a development process to define a few top-level concepts and a few specific concepts. The first step is to define the top-level concepts. The top-level concepts represent the most general concept, encompassing all entities or objects within the domain (Lopes et al., 2022). In the domain of flavouring as shown in Table 4, we identified four top-level classes through discussion with the domain experts regarding the competency questions mentioned in Table 1 and also from the output from brainstorming session with domain experts, which is a list of basic terms for the flavouring ontology. The four top-level classes for the flavouring ontology are E-Numbers, Flavouring Agent, Halal Status, and Types of Raw Material.

These four top-level classes of flavouring ontology give a general picture to the researcher for building this flavouring ontology and play an important role as the main hierarchy in the ontology development. The next step is to define the subclass (Level 1) for the top-level concepts, as shown in Table 5.

The subclasses (Level 1) for Flavouring Agents consist of four types: Bitter Agent, Salty Agent, Sour Agent, and Sweetening Agent. The ‘Sweetening Agent’ subclass was obtained directly from the hierarchy in the ChEBI ontology (Fig. 1). In contrast, the remaining subclasses were classified based on the taste criterion of the flavouring. The researcher also acquired consent from the expert regarding adding the remaining subclasses during the interview.

Fig. 1

Subclasses of flavouring agent. ChEBI, Chemical Entities of Biological Interest.

The subclasses of raw materials in Table 4 include animals, plants, and chemicals. The categorisation of raw materials was determined by the specific raw materials utilised in the production of the flavouring. These raw materials were acquired through an interview conducted with the halal management auditors in order to establish a systematic process for verifying the halal status of the flavouring (Fig. 2).

Fig. 2

Structured flow to trace halal status of flavouring.

After this, the researcher also needs to define the subclass (Level 2) for the concept ‘Chemicals,’ as shown in Table 6.

For the subclass of ‘Chemicals,’ the researcher obtained the concept of ‘Chemicals,’ which consists of ‘Alcohol’ and ‘Non-Alcohol,’ through an interview with the halal management auditors.

3.4. Conceptualisation: Define the Properties of Classes

The properties of classes need to be defined, because the classes themselves do not offer sufficient knowledge to address the competency questions listed in Table 1. Therefore, once we have defined the classes, we must also define the properties of the classes as well. There are two types of properties: data properties and object properties. The sources of information for these two types of properties are based on Fenaroli’s Handbook of Flavours Ingredients, ChEBI Ontology, and E-Numbers websites. The data properties connect individuals with some values. The list of data properties is shown in Table 7.

On the other hand, the object properties connect individuals with individuals. The list of object properties is shown in Table 8.

The object property hasSuggestedHalalStatus is obtained through an inferencing process where the researchers developed five rules to generate the halal status for a flavour. These rules were developed based on the halal conditions in the Malaysian Halal Certification Manual, which the halal management auditors explained to the researchers. The rules and their explanation are shown in Table 9.

The primary factor involved in predicting the halal status of flavourings is the raw components used. These five rules were formulated based on the categorisation of raw elements found in the flavouring agents, including animal, plant, and chemical substances. Regarding flavouring agents derived from animals, we establish two rules: If the flavouring agent is obtained from an animal other than pork, the halal status of the flavouring is likely halal; nevertheless, if the flavouring agent is derived from pig, the halal status of the flavouring is haram. Then, regarding flavouring agents derived from plants, we provide a single rule: If a flavouring agent is derived from a plant, its halal status is considered halal. Lastly, we have established two rules regarding the use of chemical-derived flavouring agents: If the flavouring agent is derived from alcohol, its halal status is considered halal under certain conditions, and if the flavouring agent is derived from a non-alcoholic chemical, its halal status is considered halal.

4.1. Implementation of the Flavouring Ontology into the Halal Status Flavouring Traceability System

After completing the modelling of the flavouring ontology, the ontology is integrated into the Halal Status Flavouring Traceability System. Fig. 3 shows an example of a search result for flavouring information.

Fig. 3

Search result of flavouring agent from Halal Status Flavouring Traceability System.

Based on Fig. 3, the search result for the flavouring agent Isovaleric Acid consists of metadata of flavouring, which are: ‘Synonym,’ ‘Raw Materials,’ ‘Description,’ ‘Botanical Name,’ ‘Natural Occurrence,’ ‘Synthesis,’ and ‘Suggested Halal Status’ (Fig. 4). The search result for flavouring agent also provides information about the flavour’s hierarchy that helps auditors to know the classification of flavouring agents, and also the hierarchy about types of raw material for flavouring agent that helps auditors to know the raw materials of flavouring agent. As for the metadata regarding ‘Suggested Halal Status’ as shown in Fig. 4, it is generated due to the inferencing rules discussed in Table 9.

Fig. 4

‘Suggested Halal Status’ metadata of flavouring agents from Halal Status Flavouring Traceability System.

4.2. Evaluating Flavouring Ontology through Halal Status Flavouring Traceability System

The flavouring ontology was evaluated using a Halal Status Flavouring Traceability System prototype. An evaluation of use in an application was proposed by Noy and McGuinness (2001) and implemented in the works of Porzel and Malaka (2004) and Kalfoglou and Hu (2006). The evaluation was carried out by soliciting comments from domain experts purposively selected after using the prototype. The involvement of domain experts during the evaluation process was to ensure the usability and practicality of the ontology for the Halal Status Flavouring Traceability System. The domain experts may evaluate the compatibility of the ontology with their processes in predicting the halal status of flavours, specifically for processing applications for halal certification from food manufacturers, by providing valuable comments on this matter. A total of nine experts participated in this evaluation: three lecturers from the Faculty of Information Science and Technology, Universiti Kebangsaan Malaysia, who are experts in ontology engineering; three lecturers from the Faculty of Science and Technology Universiti Kebangsaan Malaysia, who are experts in the flavouring domain; and three experts from the Halal Management Division of Department of Islamic Development Malaysia, recognized for their expertise in the halal certification process. The involvement of nine experts for this evaluation is to ensure a comprehensive and diverse assessment of the ontology. By involving a panel of experts with varied backgrounds and expertise, including auditors from JAKIM’s Halal Management Division and researchers with technical knowledge in ontology mapping, the evaluation process can benefit from a range of perspectives and insights. This multi-faceted evaluation approach allows for a thorough examination of the ontology’s effectiveness in predicting the halal status of flavours and its practical utility in the context of halal certification processes. Additionally, the inclusion of multiple experts helps in validating the ontology and ensuring its credibility and trustworthiness. Assessing the ontology based on using a prototype involved three evaluation criteria: Completeness, Clarity, and Preciseness.

According to Tankeleviciene and Damasevicius (2009), completeness refers to the condition where all parts of an ontology are present and each element is thoroughly explained. The completeness of the flavouring ontology is assessed based on the comprehensiveness of the concepts found. The evaluation results provided by experts indicate that the flavouring ontology lacks sufficient data on flavouring and requires improvement. For instance, raw materials and natural occurrences require more information. Other recommendations by the experts are as follows:

The concept of clarity can be described as the measure of how successfully the intended message is conveyed (Tankeleviciene & Damasevicius, 2009). The clarity of the flavouring ontology is determined by the degree to which the terminologies contained within it are clear and comprehensible. The experts’ evaluation findings indicate a need for more clarity in the flavouring ontology’s representation of flavouring data. For example, for the ‘Suggested Halal Status’ data, if the status of a flavouring is ‘Haram’ (i.e. forbidden), it is necessary to state the reason why the flavouring is ‘Haram.’

Lastly, the concept of preciseness is characterized by the presence of accurate definitions and hierarchies within an ontology, resulting in a reduced number of unwanted models (Tankeleviciene & Damasevicius, 2009). The preciseness of the flavouring ontology is evaluated based on the presence of appropriate terms inside the ontology. However, some of the metadata about flavours are not accurate. For example, Butanoic Acid is listed as a synonym for Neryl Isovalerate, which is incorrect. Another example is the categorization of glycine as haram, which is not factually correct, as glycine is an amino acid that may be found in a wide range of sources, not exclusively derived from pigs. In order to ensure precision, it is advisable for researchers to collaborate with professionals to acquire reputable references that may be utilised for the development of the flavouring ontology.