Home > Articles > Data

  • Print
  • + Share This
This chapter is from the book

This chapter is from the book

Modeling Common Relations

As you gather requirements and design a document database, you will likely find the need for one or more of three common relations:

  • One-to-many relations
  • Many-to-many relations
  • Hierarchies

The first two involve relations between two collections, whereas the third can entail an arbitrary number of related documents within a collection. You learned about one-to-one and one-to-many relations previously in the discussion of normalization. At that point, the focus was on the need for joins when normalizing data models. Here, the focus is on how to efficiently implement such relationships in document databases. The following sections discuss design patterns for modeling these three kinds of relations.

One-to-Many Relations in Document Databases

One-to-many relations are the simplest of the three relations. This relation occurs when an instance of an entity has one or more related instances of another entity. The following are some examples:

  • One order can have many order items.
  • One apartment building can have many apartments.
  • One organization can have many departments.
  • One product can have many parts.

This is an example in which the typical model of document database differs from that of a relational database. In the case of a one-to-many relation, both entities are modeled using a document embedded within another document. For example:

{
   customer_id: 76123,
   name: 'Acme Data Modeling Services',
   person_or_business: 'business',
   address : [
                     { street: '276 North Amber St',
                        city: 'Vancouver',
                        state: 'WA',
                        zip: 99076} ,
                     { street: '89 Morton St',
                        city: 'Salem',
                        state: 'NH',
                        zip: 01097}
                    ]
   }

The basic pattern is that the one entity in a one-to-many relation is the primary document, and the many entities are represented as an array of embedded documents. The primary document has fields about the one entity, and the embedded documents have fields about the many entities.

Many-to-Many Relations in Document Databases

A many-to-many relation occurs when instances of two entities can both be related to multiple instances of another entity. The following are some examples:

  • Doctors can have many patients and patients can have many doctors.
  • Operating system user groups can have many users and users can be in many operating system user groups.
  • Students can be enrolled in many courses and courses can have many students enrolled.
  • People can join many clubs and clubs can have many members.

Many-to-many relations are modeled using two collections—one for each type of entity. Each collection maintains a list of identifiers that reference related entities. For example, a document with course data would include an array of student IDs, and a student document would include a list of course IDs, as in the following:

Courses:

{
  { courseID: 'C1667',
     title: 'Introduction to Anthropology',
     instructor: 'Dr. Margret Austin',
     credits: 3,
     enrolledStudents: ['S1837', 'S3737', 'S9825' ...
       'S1847'] },
  { courseID: 'C2873',
     title: 'Algorithms and Data Structures',
     instructor: 'Dr. Susan Johnson',
     credits: 3,
     enrolledStudents: ['S1837','S3737', 'S4321', 'S9825'
       ... 'S1847'] },
  { courseID: C3876,
     title: 'Macroeconomics',
     instructor: 'Dr. James Schulen',
     credits: 3,
     enrolledStudents: ['S1837', 'S4321', 'S1470', 'S9825'
       ... 'S1847'] },
  ...

Students:

{
 {studentID:'S1837',
   name: 'Brian Nelson',
   gradYear: 2018,
   courses: ['C1667', C2873,'C3876']},
 {studentID: 'S3737',
   name: 'Yolanda Deltor',
        gradYear: 2017,
        courses: [ 'C1667','C2873']},
    ...
}

The pattern minimizes duplicate data by referencing related documents with identifiers instead of embedded documents.

Care must be taken when updating many-to-many relationships so that both entities are correctly updated. Also remember that document databases will not catch referential integrity errors as a relational database will. Document databases will allow you to insert a student document with a courseID that does not correspond to an existing course.

Modeling Hierarchies in Document Databases

Hierarchies describe instances of entities in some kind of parent-child or part-subpart relation. The product_category attribute introduced earlier is an example where a hierarchy could help represent relations between different product categories (see Figure 8.11).

Figure 8.11

Figure 8.11 Hierarchies describe parent-child or part-subpart relations.

There are a few different ways to model hierarchical relations. Each works well with particular types of queries.

Parent or Child References

A simple technique is to keep a reference to either the parent or the children of an entity. Using the data depicted in Figure 8.11, you could model product categories with references to their parents:

{
   {productCategoryID: 'PC233', name:'Pencils',
     parentID:'PC72'},
   {productCategoryID: 'PC72', name:'Writing Instruments',
     parentID: 'PC37''},
   {productCategoryID: 'PC37', name:'Office Supplies',
     parentID: 'P01'},
   {productCategoryID: 'P01', name:'Product Categories' }
}

Notice that the root of the hierarchy, 'Product Categories', does not have a parent and so has no parent field in its document.

This pattern is useful if you frequently have to show a specific instance and then display the more general type of that category.

A similar pattern works with child references:

{
   {productCategoryID: 'P01', name:'Product Categories',
     childrenIDs: ['P37','P39','P41']},
    {productCategoryID: 'PC37', name:'Office Supplies',
      childrenIDs: ['PC72','PC73','PC74'']},
     {productCategoryID: 'PC72', name:'Writing
       Instruments', childrenIDs: ['PC233','PC234']'},
      {productCategoryID: 'PC233', name:'Pencils'}
}

The bottom nodes of the hierarchy, such as 'Pencils', do not have children and therefore do not have a childrenIDs field.

This pattern is useful if you routinely need to retrieve the children or subparts of the instance modeled in the document. For example, if you had to support a user interface that allowed users to drill down, you could use this pattern to fetch all the children or subparts of the current level of the hierarchy displayed in the interface.

Listing All Ancestors

Instead of just listing the parent in a child document, you could keep a list of all ancestors. For example, the 'Pencils' category could be structured in a document as

{productCategoryID: 'PC233', name:'Pencils',
  ancestors:['PC72', 'PC37', 'P01']}

This pattern is useful when you have to know the full path from any point in the hierarchy back to the root.

An advantage of this pattern is that you can retrieve the full path to the root in a single read operation. Using a parent or child reference requires multiple reads, one for each additional level of the hierarchy.

A disadvantage of this approach is that changes to the hierarchy may require many write operations. The higher up in the hierarchy the change is, the more documents will have to be updated. For example, if a new level was introduced between 'Product Category' and 'Office Supplies', all documents below the new entry would have to be updated. If you added a new level to the bottom of the hierarchy—for example, below 'Pencils' you add 'Mechanical Pencils' and 'Non-mechanical Pencils'—then no existing documents would have to change.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020