PartMain      - o:m Section, o:m Report
PartSection   - m:o Main, o:m Property
PartProperty  - m:o Section, Contains MainID for sorting purposes, SortByMainID
PartReport    - m:o Main

PartMain: Name, Desc, etc... rest of data
    PartSection1: data...
        PartProperty1: data.. (all properties in relationship with that section)
    PartSection2: data... (all sections in relationship with selected PartMain)
        PartProperty1: data.. (all properties in relationship with that section)
    PartReport: data.... (all reports with selected PartMain)

pMainID = selectedMainID;
PartMain partMain = db.PartMain.Find(pMainID);
ViewBag.Name = partMain.Name
ViewBag.Desc = partMain.Desc

var partSections = db.PartSection.Where(s => s.pMainID = pMainID);

foreach (var partSec in partSections)
{
    ViewBag.PartSecName = partSec.Name
    ViewBag.PartSecDesc = partSec.Desc

    var partProperties = db.PartProperties.Where(p => p.pSecID = partSec.ID);
    foreach(var partProp in partProperties)
    {
        ViewBag.PartPropName = partProp.Name
        ViewBag.PartPropDesc = partProp.Desc
    }
}

var pMainID = selectedMainID;
PartMain partMain = db.PartMain.Find(pMainID);

ViewBag.Part = partMain;

ViewBag.Sections = db.PartSection
    .Where(s => s.pMainID = pMainID)
    .Select(s => new
    {
        Section = s,
        Proeprties = db.PartProperties.Where(p => p.pSecID = partSec.ID)
    });

<h1>@ViewBag.Part.Name</h1>
<p>@ViewBag.Part.Desc</p>

@foreach(var section in ViewBag.Sections)
{
    <h2>@section.Section.Name</h2>
    <p>@section.Section.Desc</p>

    <dl>
    @foreach(var property in section.Properties)
    {
        <dt>@property.Name</dt>
        <dd>@property.Desc</dd>
    }
    </dl>
}